Authenticity screening of stained glass windows using optical spectroscopy
Civilized societies should safeguard their heritage as it plays an important role in community building. Moreover, past technologies often inspire new technology. Authenticity is besides conservation and restoration a key aspect in preserving our past, for example in museums when exposing showpieces. The classification of being authentic relies on an interdisciplinary approach integrating art historical and archaeological research complemented with applied research. In recent decades analytical dating tools are based on determining the raw materials used. However, the traditional applied non-portable, chemical techniques are destructive and time-consuming. Since museums oftentimes only consent to research actions which are completely non-destructive, optical spectroscopy might offer a solution. As a case-study we apply this technique on two stained glass panels for which the 14th century dating is nowadays questioned. With this research we were able to identify how simultaneous mapping of spectral signatures measured with a low cost optical spectrum analyser unveils information regarding the production period. The significance of this research extends beyond the re-dating of these panels to the 19th century as it provides an instant tool enabling immediate answering authenticity questions during the conservation process of stained glass, thereby providing the necessary data for solving deontological questions about heritage preservation.
Window glass composition changes throughout time1. Major compositional groups within the wood and plant tradition (~800–1800 AD) are defined based on differences in calcium, potassium and sodium concentration and include potash, high lime low alkali (HLLA) and mixed-alkali glass2. Medieval glasses in the Low Countries typically have a potash composition. At the end of the 15th century the potash type was gradually abandoned in favour of the HLLA glass. From the end of the 17th century to the early 19th century, most window glass is mixed-alkali3. Subsequently in the 19th century industrial produced soda is used for glass manufacturing4,5.
Stained glass windows typically hold an assemblage of coloured pieces. Depending on the production phase, the individual panes are classified as being naturally-coloured, pot-coloured or flashed. Unintentionally (natural) colouring arrives from metal impurities in the raw materials. Intentionally colouring is imposed by adding metal oxides; pot-coloured glass refers to body-tinted glass while flashed glass is composed of a clear glass flashed with one or multiple thin coloured glass layers.
On top of the glass decoration layers based on painted details in combination with yellow stain are often applied to enhance the design. The use of silver stain is omnipresent in the 14th century and became generally applied in the 15th and 16th century6. The procedure consists of coating the glass surface with a silver compound dispersed in a clay medium and firing at a temperature just above the glass transition temperature. During this process silver ions are exchanged with the alkali ions from the glass (Na+ or K+) and diffuse in the glass. Subsequently they reduce to the metallic state with the growth of silver nanoparticles. The diffusion coefficients and the redox reactions depend on the composition of the glass. In addition, also the production parameters (firing temperature and time) as well as the composition of the coating play an important role in the staining process. The colour depends on the size, shape and concentration7 and is the result of localized absorption and scattering. The recipe of silver stain was first described by Antoine de Pise, only using silver8. In the late 15th century the interest to obtain brighter yellow and orange colours grew and the combined use of silver and copper was exploited to increase the size of the colloids and broaden the colour range6.
The above described chronological differences in glass composition, make that authenticity questions of stained glasses often go hand-in-hand with the study of the window’s composition. In recent years attention focused on non-destructive and portable analysis methods for measuring glass composition. This as a replacement for the electron- or X-ray based analytical techniques such as Wavelength-Dispersive X-ray spectrometry (SEM-WDS), Electron Probe Micro-Analysis (EPMA), or Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) which require expensive laboratory equipment and sample pre-treatment. Technological developments led to the use of handheld X-Ray-Fluorescence (XRF) equipment9,10, mobile instruments for Raman analysis11,12 and portable spectrophotometers13. Our team has proven the advantages of applying UV-VIS-NIR spectroscopy as a first-line analytical technique. It is fast and relatively cheap, essentially non-destructive and it can be used in-situ by trained art historians and archaeologists13,14,15,16. Since the colouring agent signature depends on the composition of the glass, optical absorption spectroscopy can be used as a first-line technique to unveil information about the glass composition of coloured glasses. The purpose is to relate a specific glass composition to a characteristic spectral pattern consisting of one or several absorption bands located at well-defined spectral wavelengths. These absorption bands are the spectral fingerprint of the transition metals. So far all our cases have been limited to the study of naturally-coloured or pot-coloured glasses. The use of UV-VIS-NIR spectroscopy as archaeometric analysis tool has already been applied to identify the pigments in several other types of ancient materials such as ceramics and glazes17,18, paintings19, paper and ink artefacts20 as well as stone monuments and wall paintings21.
The objective of this paper is to verify if UV-VIS-NIR spectroscopy can be used to give a conclusive answer when dating stained windows. Therefore, we need to extend our domain of expertise from the study of pot-coloured and naturally-coloured glasses to spectral research on flashed and stained glasses. As a case-study we investigate two remarkable intact stained glass panels in the permanent exhibition of the museum ‘Ten Duinen 1138’, which is located on the ruins of the former medieval Cistercian Abbey of the Dunes at Koksijde (Belgium). The two panels are believed to be authentic architectural canopies from two different windows of the former abbey that was founded in the 12th century and abandoned around 1600. In the early 1960’s both panels were dated to the 14th century by the art historian Jean Helbig22. His conclusions were solely based on stylistic similarities with the windows of the church Saint-Ouen in Rouen (France) dated to 1325; and the windows of Klosterneuburg Monastery (Austria) dated around 1330. However, as it is commonly known that ancient motifs were frequently copied in later periods, it is not surprising that archival research we conducted unveiled several neo-gothic (19th – early 20th c.) windows with similar stylistic characteristics. Two additional visual observations strengthen the questioning of a 14th century origin of the panels: (1) The glass is physically very complete and the environment has not taken its toll over centuries. A detailed survey highlights a complete absence of any weathering of the glass or painted surfaces. If the glass would be 14th century material, then the condition of the potash rich glass would have been highly deteriorated displaying extensive traces of corrosion23. (2) The lead cames are not comparable to 14th century material. The flanges of the cames demonstrate characteristic regular-shaped cross-sections and the core of all lead cames show clear and straight parallel tooth marks both coming from the milling process24. Although the exact date of invention of the mill remains unclear, written sources hint at the later 15–16th century.
Since none of the mentioned macroscopic observations is fully conclusive, we further investigate all 85 panes of the two glass panels by optical spectroscopy. The methodology is to discover the fabrication date by unravelling the applied glass composition via the study of the spectral properties of the different groups; i.e. pot-coloured, flashed, naturally-coloured and stained glass. The research is divided in two parts. A first focus is put on flat glass as a canvas. For the pot- and naturally-coloured fragments emphasis is put on the study of the metal oxide absorption bands. For the flashed glasses we analyse the nanoparticle properties (type and dimensions) and compare them with the properties of a collection of historic flashed samples for which a similar metal was applied for colouring. The selected samples cover a range of different glass compositions. For the investigation of the decoration layers we follow an analogue approach; we investigate the spectral properties of the silver stained pieces and verify if the spectral properties match with those of well-dated historic samples described in literature.
Setup of the panels
The panels (Fig. 1) show architectural canopies from two different windows, both designed in complete symmetry. For four panes it is known that they were restored (54–9, 54–22, 54–31 and 55–4).
Technical examination by optical spectroscopy
As a first step all measured spectra are classified in separate groups based on the observed spectral shapes. In the coming part of the paper we will refer to the spectral groups rather than to the pane numbers in order not to overload the text. Supplementary Table 1 summarizes the spectral features of each individual pane including the CIE1931 colour value (see paragraph on methods).
Intentionally pot-coloured panes
The classification based on overall spectral shape of the spectra belonging to the blue panes leads to three groups B1–3 (Fig. 2). Maximum transmission occurs between 350–500 nm; the three groups differ in spectral position of the transmission maximum with averaged values of respectively 456.0 (±1.4), 459.6 (±1.7) and 393.0 (±1.4) nm. Analysis of the absorbance spectra indicate the presence of cobalt as colouring element. Cobalt is characterised by the presence of three successive absorption bands close to 535 nm, 596 nm and 640 nm attributed to the Jahn-Teller split transition A2 → T1(P) of Co2+ tetrahedral coordinated by four oxygen ions25. In all spectra of the blue fragments these bands are visible. Apparent is the common spectral position of the first cobalt absorption band of all blue fragments close to 534.2 nm (±1.6). Ceglia et al. correlates the spectral shift of this band to the composition of the historical glass26. Glasses with a calco-potassic composition have a band situated around 526.5 nm (±1.5 nm) shifting towards longer wavelengths (535 nm ±2 nm) in case of a soda based composition. These observations correspond with those made by Green and Hart27. Therefore, we conclude that the blue panes contain cobalt as colouring agent in a soda containing glass matrix and thus we can exclude a 14th–15th century origin.
An important element for dating green pot-coloured panes is chromium; an element which typically distributes into a trivalent Cr3+ and a hexavalent Cr6+ state. The trivalent state is characterized by several absorption bands in the visible region which correspond to the d-d spin allowed ligand field transitions and results in an emerald green colour. The hexavalent state owes one strong charge transfer band in the ultraviolet part of the spectrum and imparts a lemon yellow colour. Scholars report data on the spectral positions of both ion states all referring to the pioneering work of Bamford, Weyl and Nath and Douglas28,29,30. The glass fragments used in these references are custom made glass fragments and include lithium, sodium and potash silicate glasses. In sodium silicate glasses the absorption peaks are found to be centred around 450 nm, 633 nm, 646 nm and 682 nm for Cr3+ and at around 365 nm for Cr6+. The presence of a sufficient amount of Cr6+ most often masks the Cr3+ absorption peak at around 450 nm. Unfortunately, the differences in spectral positions of the absorption peaks in different glass matrices are smaller than 5 nm. Therefore, inferences on the glass matrix based on the analysis of the spectral positions of the chromium absorption bands are useless. However, as it is generally believed that the exploitation of chromium as colouring element in glass industry only starts from the second half of the 19th century onwards, we can focus our research to the identification of the presence/absence of the chromium signature. However, the fact that chromium could also enter the glass batch via the cobalt ores has to be taken into account.
All the green panes show maximum transmission close to 530 nm (Fig. 3). Spectral analysis unveils two groups G1–2 due to a different spectral position of the transmission maximum respectively at 539.3 (±2.1) and 522.5 (±1.4) nm. The above mentioned Cr3+ bands are visible in all absorbance spectra. In addition, it appears that they contain a considerable amount of Cr6+. Accordingly, the corresponding absorption band around 365 nm is clearly visible influencing the strength of the Cr3+ absorption band at 450 nm. In Fig. 3 we demonstrate how the observed chromium absorption bands of pane N°54 coincide with those of a reference sample B1S4 for which the presence of chromium was proven via SEM-EDX analysis (Supplementary Table 2). The linear absorption coefficient of cobalt is large (approximately a factor of five for soda-silica-lime) compared to other metal oxides. This makes that the presence of trace levels of cobalt can easily be optically detected. Since we did not observe any cobalt absorption band in the recorded optical spectra we conclude that it is unlikely that the chromium oxides entered the batch as trace element originating from cobalt ores. We assume that the glasses were intentionally coloured with chromium. Therefore we conclude that the green pieces cannot be dated before the second half of the 19th century.
Yellow glass is used for the border parts of both panels. The panes of panel N°55 are close to the yellow-white boundary of the horse-shoe colour diagram. Five separate spectral groups are recognized (Fig. 4). The first two groups are characterized by the presence of the main Fe2+ absorption peak and by weak Co2+ absorption bands. The main absorption band of Fe2+ is close to 1000 nm. Groups Y1–2 differentiate by their spectral position of the transmission maximum respectively at 711.9 (±3.1) nm and 697.5 (±1.4) nm. The spectral shape of the third group (Y3) indicates the presence of Fe3+ with absorption bands close to 380, 420 and 440 nm. These spectra are purer with gradual decreasing absorbance values starting from 450 nm onwards and converging to a constant level at a wavelength close to 1000 nm. Also the contour parts of panel N°55 are mainly coloured by the presence of Fe3+ ions. These fragments are classified in two groups (Y4–Y5) distinguished by the spectral position of the transmission maximum (605.4 ± 10.6 nm and 685.5 ± 1.4 nm). The presence of an additional band close to 800 nm for the fourth group (Y4) is probably caused by the presence of Cu2+ ions. Since no link has currently been uncovered between differences in Fe2+/Fe3+ ratio and the absence/presence of Co2+ and Cu2+ ions and the glasses’ chronological or geographical origin, we cannot draw any conclusion on the date of production of the yellow parts. Nevertheless, the authors decided to include the spectroscopic data to enable the immediate validation of this data in case future developments related to this issue are made by us or other research groups.
Panel N°54 contains ten red panes. The characteristic copper surface plasmon resonance (SPR) peak, clearly visible in the measured spectra (Fig. 5), confirms the presence of Cu0 nanoparticles. The reduced glasses show a narrow peak at 563.1 (±0.8) nm generated by the colloidal dispersion of the metallic nanocrystals in the glass and a broader spectral contribution centred at 430 nm. The latter is usually correlated with isolated Cu0 atoms in the glass31. Although all ten samples have a quite similar spectral shape, some differences in peak intensity are observed. The peak at 430 nm is most distinct for fragment 54–44 and is weaker but still clearly observable for parts 54–13, 54–19, 54–20 and 54–40. It is absent for the remaining panes. The position of the SPR peak together with the slope of the absorbance curves between 400–500 nm points out the absence of europium ions31.
The colour uniformity observed by naked eye and with a magnifying glass indicates an even size distribution of the nanoparticles and favours a classification in the so-called ‘plaqué type’ structural group. The absence of the typical ‘wavy’ pattern due to the presence of red striae brought us to the conclusion that a sandwich structure is unlikely. We drew this conclusion based on the work described by Jerzy J. Kunicki-Goldfinger32 in which the macroscopic observation of the presence of a sandwich structure was confirmed via TEM examination. However in our case TEM examination was not possible as the museum stipulated solely fully non-destructive research. As a consequence no sampling, or any gentle material preparation was allowed.
The average cluster radii R of the embedded nanoparticles are calculated from the full-width half-maximum (FWHM) of the optical absorption peaks using an extrapolation of the formula provided by Manikandan33. The average particle radius of 11.0 (±0.7) nm agrees with the particle sizes described by Kunicki-Goldfinger32.
The position and shape of the SPR band depends on the structure and distribution of the clusters as well as on the dielectric functions of the metal- and the glass matrix and the annealing temperature. From Manikandan’s research33 we know that in case of copper nanoparticles in soda lime glasses there is a blue shift of the SPR wavelength and a decrease in particle size (FWHM increases) with increasing annealing temperature. These findings were in agreement with the research of Kreibig and Vollmer7. In an attempt to gather more information on the production technique and period, we compared these values with the dispersion properties and quantum dot sizes of all other red copper fragments studied by our research group in the past decade. Despite the limited number of studied fragments some conclusions can be drawn when plotting the nanoparticles radii R as a function of the FWHM values (Fig. 6). The correlation between both parameters is clearly visible and highlighted by plotting trend lines. A difference in slope is observed for the potash, HLLA and soda glasses. We consider two groups of HLLA material (see Supplementary Table 2) classified mainly on differences in alkali metal concentration levels. All the samples taken from the two panels fit to the FWHM-R trend line of the soda rich material. Both groups also have matching SPR peak position values (Supplementary Table 1). However, the latter is not conclusive; the SPR values of the soda rich material are blue shifted compared to the HLLA material but have quantitative similar values as the potash fragments.
The spectroscopic properties exclude a pure potash rich as well as a pure soda rich glass composition and favours a mixed-alkali glass composition for the red pieces. This fact rules out a 14th century origin which would favour a pure potash rich composition. However, the presence of potash ions rejects the assumption that we are dealing with modern panels fabricated during the industrial period which would imply a pure soda rich composition. Along with the blue and green fragments, we can conclude that also the red flashed parts cannot be dated to the 14th century.
These fragments cover the centre part of the horse-shoe curve and can be classified in four spectral groups (Fig. 7). A first group P1, containing panes from both panels, is characterized by several absorption bands whose positions close to 381 nm, 446 nm, 638 nm, 644 nm and 686 nm indicate the presence of Fe3+ and Cr3+. The three fragments of panel N°55 correspond to the white glass decorated with silver yellow. The second group P2 contains white quarries both with and without silver stain. Also here we observe different spectral absorption bands. The discerned spectral positions at 380 nm, 418 nm, 594 nm, 641 nm and 684 nm designate the manifestation of chromium, cobalt and/or iron traces. The panes of the remaining two groups show a much cleaner profile with an almost lack of trace element bands. The plain fragments of the third group P3 have large absorbance values possibly caused by the presence of grisaille paint traces. The single fragment of the last group P4 displays the typical ferrous absorption band close to 1050 nm. The absorption band at 418 nm suggests the formation of an iron-manganese complex34. The fact that the naturally-coloured parts display a rather impure composition reflected by the presence of several trace elements, makes it very unlikely that the non-coloured parts are fabricated with an industrial controlled procedure since modern, industrial glasses are typically characterized by a very pure composition.
Silver stain decorations
Both panels contain several silver stained fragments. Study of the spectral signatures reveals four separate groups: SY1–4 (Fig. 8). All spectra of SY1–3 are characterized by an almost coincident spectral position of the absorption maximum close to 419.4 (±2.9) nm. The classification is based on a difference in spectral bandwidth ranging between 22.5–75 nm. In the case that the silver stain pieces were fabricated under equal firing temperatures, the appearing coincident absorption peak maxima values might indicate a similar firing temperature with the difference in FWHM pointing out a change in particle dimensions. Using Doyle’s formula35 the calculated corresponding average cluster radii R span 1.8–5.7 nm. Since almost the entire central motif is decorated with silver stain belonging to SY1–2, hypothetically it is plausible that both groups contain an equal glass type and reflect the genuine manufacturing of the panel. SY3 spectra demonstrate a clear second (weaker) blue shifted band between 380–450 nm. This band is already visible in the second group of panes; though at a much lower intensity. Mock et al.36 describes the development of a single band due to a formation of spherical particles while the appearance of two bands may originate from either a bi-modal distribution of nearly spherical particles or a distribution of particles with non-spherical symmetry. Currently the cause of the appearance of this second band remains an open question. Referring to the spectral similarities of the SY1–3 stained fragments a possible explanation might be that the double shifted peaks are caused by a higher density of particles6 and the groups simply correspond to the use of different concentrations of precursor mixture. The SY4 stained fragments have a deviant spectral shape. The peak maxima are red shifted near 428.2 (±2.6) nm and the broad band with FWHM value close to 67 nm has a tail towards the 450–550 nm region. This shape leads to an orange hue which might indicate the use of clays35 or the presence of a mixture of Ag and Cu in the paste composition37. The strong correlation in spectral shape of these spectra with the laboratory-made glass fragments reported in Delgado’s paper37, favours the second option.
A variety of mainly fabrication and material related parameters determine the final colour. At present only a few authors have applied the silver stain process on custom-made glasses in order to unveil the fabrication techniques in medieval times. The limited amount of research at this stage makes a decision about fabrication conditions and corresponding period based on colour and spectral shapes difficult. However, since each fabrication condition (glass type, paint type and concentration, firing temperature and time) leads to a characteristic spectral fingerprint we compared the colour and spectral shapes of all SY1–4 stained glasses with those of ancient fragments found in literature. The glass compositions of these fragments include HLLA and mixed-alkali; two of the three major glass types used between 800–1800 AD. It concerns ten HLLA fragments from two Spanish (Avila & Palencia)6 (Avi15, Avi16 and Pal15) and one Belgian (Bruges)38 location together with three (O3, O5 and O13) mixed-alkali pieces from Tomar (Portugal)37. The HLLA samples from Bruges are further classified in HLLA1 and HLLA2 following their differences in alkali metal concentration levels. Chemical data is given in Supplementary Table 2. Three observations are made. (1) Apart from the two samples originating from Avila, the calculated colour values group all fragments in three separate classes characterized by a greenish-yellow, yellow or orange colour (Fig. 9). (2) Secondly, it is perceived that the colour values as well as the entire spectral shape of the three mixed-alkali fragments correspond pretty well with the stained fragments of the two studied panels. (3) Finally, it is concluded that the standard deviations on the spectral properties (error flags in Fig. 10) of the latter are much smaller compared to the two HLLA groups of post-medieval material. This points out a better controlled fabrication process potentially implying a more recent production.
Several types of silver compounds can be used affecting the final appearance. Jembrih-Simbürger39 has proven that the silver compound type affects the distribution of the particles resulting in uniform or speckled layers. Since none of the stained panes show a speckled surface, the silver salt was most probably AgNO3. In addition, comparison of the spectral data with the samples described by Pérez-Villar35 did not unveil any similarity favouring the idea of the absence of clay in the silver mixture. Jembrih-Simburger39 also reports on the relation between colour intensity, applied silver salt and firing temperature. More in particular the silver compounds are divided in three groups: (1) silver compounds resulting in an intense colour at low firing temperatures such as AgNO3 and Ag2SO4; (2) compounds resulting in a paler colour at low firing temperatures such as AgCl and Ag3PO4; and (3) compounds that hardly result in any colour such as Ag2O. The information given in this paper together with the analysed colours and defined silver salt predicts a low firing temperature for the two panels. As the staining process takes place at a temperature close to the glass transition temperature, this implies a mixed alkali or a soda rich composition; a conclusion which is based on the glass transition temperatures reported in literature (533 °C mixed alkali glass35; 564 °C soda lime glass; 653 °C high lime low alkali glass6).
We conclude that these data give an additional prove of non-authenticity; the presence of a Cu-Ag mixture in the glass paint suggests that the pieces were not produced before the 16th century. Three factors strengthen the assumption of a mixed-alkali composition suggesting a fabrication date between the end of the 17th century and the start of the industrial glass production from the mid 19th century onwards: (1) The fabrication process of the silver stained parts of the two panels seems to be more controlled compared to earlier dated glasses with a HLLA composition (end 15th–end 17th century); (2) The similarity in spectral properties between the stained fragments of the two panels and historic well-dated fragments with a mixed-alkali composition and (3) Staining process temperatures which are close to the glass transition temperature of mixed-alkali glasses. Finally, there is also an additional prove for a non-industrial fabrication being the absence of selenium, europium and cadmium nanoparticles commonly used in 20th century red stained glasses.
Dating criteria discussion
Several identified spectral groups contain fragments from both panels. Therefore, it is most likely to date both panels in a similar period.
The spectroscopic research outcome excludes an early 14th century origin because of three main reasons: the absence of a pure potash rich glass composition, the presence of colouring elements or fabrication techniques only used in later periods and the evidence of a rather controlled fabrication process leading to quite uniform spectral shapes with small deviations within one group.
The spectral position of the cobalt absorption bands of all blue fragments and the copper nanoparticle signatures of all red flashed glasses indicate a soda rich nature.
The presence of chromium dates all green pieces in a recent period. Kunicki-Goldfinger et al.32 described a chronological occurrence of flashed red plaqué glasses from the late fourteenth century onwards. Although this concerned a study of British and French material, a geographical expansion is not illusive. Twenty-five percent of the silver stained fragments seems to be painted with a Cu-Ag mixture. Following Molina6 this would mean that these pieces were not produced before the sixteenth century.
The spectral properties indicate that not all red parts were placed at the same time or that they originate from different plates. Though, their close position on one straight line in the FWHM-R scatter plot denotes similar fabrication conditions.
Seventy-five percent of all silver stained fragments have almost coincident positions of the peak maxima indicating a similar firing temperature. The tail spreading differences between the three subgroups points to a change in precursor mixture concentration. In addition, it can be concluded that the standard deviations for all four silver stained groups of Koksijde are small compared to the two HLLA groups of post-medieval material from Bruges. This might point out a better controlled fabrication process for the Koksijde material.
Several observations hint a mixed-alkali glass composition. For the silver stained fragments the strong correlation in spectral shape with the mixed-alkali samples from Tomar is distinct.
If we indeed assume that we are dealing with AgNO3 silver salts for the Koksijde material and taking into account that the staining process takes place at a temperature close to the glass transition temperature, this would imply a mixed alkali or a soda rich composition. The spectral similarities of the Ag-Cu silver stained fragments with the custom-made fragments of Delgado unveils the presence of potash atoms. Since earlier conclusions also proofed a presence of soda atoms, a soda-potash mixture is plausible. In addition the absence of red colouring nanoparticles such as selenium, europium and cadmium commonly used in the early 20th century31,40 voids a pure industrial-based soda rich glass composition. Yet another fact that strengthens this allegation is the rather impure plain glass composition. The presence of trace elements possibly introduced via a wood ash based flux almost excludes a potential glass fabrication of these fragments within a highly controlled industrial environment.
Although the precise boundaries of production date still need some refinement, it is generally accepted that mixed-alkali glasses can be roughly dated between the end of the 17th century until the end of the 19th century. For this particular case we make the hypothesis that the two panels are most probably produced in the second half of the 19th century. The latter is based on two specific observations: (1) the presence of chromium atoms (from second half of 19th century onwards) and (2) the absence of red colouring selenium, europium and/or cadmium nanoparticles (from the early 20th century onwards).
Since both panels form part of the museum’s permanent exhibition, all analysis steps had to be finalized within one week. For this research the panels could not be dismantled and none of the glass fragments were taken out of the lead matrix. In order to enable good measuring both panels were temporarily disembodied from their non-transparent perspex carrier. Afterwards we measured the transmission spectra of all mentioned parts. Finally the panels were replaced onto the perspex carrier.
For each defined location we recorded the transmittance spectrum T(λ) between 300–1500 nm; i.e. the spectral region where most absorption bands are located. Afterwards we calculated the absorbance spectra using the formula A(λ) = −log10T(λ). A spectral broadband light source (Avalight-HAL + DHSBAL; Avantes) illuminated the sample; an optical spectrum analyser (AvaSpec-3648, AvaSpec-256-NIR1.7; Avantes) was used to measure the transmitted intensity as a function of the wavelength. The analysed area has a circular surface area close to 10 mm2. Spectra are recorded with a spectral resolution of 1.4 nm.
For the decorations two measuring points were taken if possible, considering both the glass and the silver stain.
The external properties of the panels only allow the application of a so-called ‘relative’ measurement configuration. It uses an optical fibre with a large acceptance angle (NA = 0.22) to capture most of the transmitted light. This is in contrast with an ‘absolute’ configuration where all the transmitted light is guided towards the spectrum analyser using an integrating sphere. The consequence is that we are not able to draw quantitative conclusions about the chemical composition. This was anyway not required for this study.
Calculation of the average cluster radius R
The average cluster radii R of the embedded nanoparticles are calculated using an extrapolation of equation (1) which is the formula provided by Manikandan33:
where Vf is the Fermi velocity of the electrons in bulk metal (copper = 1.57 × 108 cm/s; silver = 1.39 × 108 cm/s), Δλ is the full-width at half maximum of the absorption band and λp is the characteristic wavelength at which surface plasmon resonance (SPR) occurs.
The colour values which we represent on the widely used CIExy 1931 colour diagram are derived from the measured transmission spectra. In a first step this spectrum is multiplied with the colour matching functions and the spectrum of the source under which we observe the object. We calculated the colour for an equal energy illumination. Next, integration of the three obtained spectra between 380–780 nm (i.e. the spectral region for which the human eye is colour sensitive) leads to three values X, Y and Z. These values result after normalization in the colour values x and y which are represented on the horse-shoe curve. All colours that are physically perceivable by the human eye can be located inside the closed figure on this graph. The curved line is the spectral locus and represents all monochromatic colours.
The work described in this paper has been a model of collaboration between art historians and optical engineers in the context of cultural heritage research. Profound re-examining of the macroscopic material properties and stylistic comparison of the two stained glass panels questioned their authenticity. In addition to the macroscopic clues, spectroscopic analysis has now confirmed the incorrect dating of both panels to the 14th century. The integrated research offers persuasive evidence that the production date of both panels is far more likely to be placed in the second half of the 19th century. As the abbey was abandoned in 1578 and further dismantled in 1625, this conclusion is of considerable significance indicating that neither of the two panels can have come from the Abbey of the Holy Mary of the Dunes. For the museum ‘Ten Duinen 1138’, this new insight will imply a redesign of the presentation of both panels, since they can no longer be presented as authentic pieces from the former Cistercian Abbey of the Dunes.
This paper therefore demonstrates the important role optical spectroscopy can play in the enigma of authenticity questions of stained glass.
How to cite this article: Meulebroeck, W. et al. Authenticity screening of stained glass windows using optical spectroscopy. Sci. Rep.6, 37726; doi: 10.1038/srep37726 (2016).
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The research leading to these results has received funding from the Vrije Universiteit Brussel in the framework of different projects (IOF-POC1 and HOA15). The authors would like to express their gratitude to the Abbey museum ‘Ten Duinen – Koksijde’ and the community council of Koksijde for granting us permission to study the two panels.
Meulebroeck Wendy and Wouters Hilde contributed equally to this work.
Applied Physics and Photonics Department, Vrije Universiteit Brussel, Brussels Photonics Team B-PHOT, Brussels, 1050, Belgium
Wendy Meulebroeck, Hilde Wouters & Hugo Thienpont
Department of Art Studies and Archaeology, Vrije Universiteit Brussel, Brussels, 1050, Belgium
Hilde Wouters & Karin Nys
H.W. performed the spectral measurements under supervision of W.M. H.W. performed the art-historic analysis; W.M. the spectroscopic data analysis. The integrated analysis was done by W.M. and H.W. and reviewed by K.N. All authors contributed to the research as a whole. W.M. and H.W. wrote the manuscript and produced all pictures and figures shown in this paper. All authors reviewed the manuscript.
The authors declare no competing financial interests.
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Meulebroeck, W., Wouters, H., Nys, K. et al. Authenticity screening of stained glass windows using optical spectroscopy. Sci Rep6, 37726 (2016). https://doi.org/10.1038/srep37726
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Stained Glass Panel with the Visitation
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On view at The Met Fifth Avenue inGallery 306
This panel was part of a window depicting the ancestry of Christ in the form of a Tree of Jesse. The painter of this window, adopting an angular style of drapery folds and subtle color juxtapositions, initiated a new style of glass painting in the Middle Rhine.
Title:Stained Glass Panel with the Visitation
Geography:Made in Germany
Medium:Pot metal, white glass, vitreous paint, silver stain, olive-green enamel
Dimensions:Overall (with 1 T-bar): 43 3/8 x 29 1/8 x 3/8 in. (110.2 x 74 x 1 cm)
a: 22 1/16 x 29 1/4 x 3/8 in. (56 x 74.3 x 1 cm)
b: 21 7/16 x 29 1/16 x 3/8 in. (54.5 x 73.8 x 1 cm)
Credit Line:Francis L. Leland Fund, 1913
Accession Number:13.64.3a, b
From the Carmelite church, Boppard-am-Rhein.; Count Hermann Pückler, Bad Muskau; [ Frédéric Spitzer, Paris (sold 1893)]; his posthumous sale, Chevallier & Mannheim, Paris (April 17–June 16, 1893, no. 3360); [ Frederick Davis & Son, London (from 1893)]; [ Duveen Brothers, London, Paris and New York]; Grosvenor Thomas, London (sold 1913)
Musée d'Unterlinden. "Jost Haller le peintre des chevaliers et l'art en Alsace au XVe siècle," September 15–December 16, 2001.
Catalogue des objets d'art et de haute curiosité: antiques, du moyen-âge & de la renaissance, composant l'importante et précieuse Collection Spitzer. Vol. 2. Paris: Chevallier and Mannheim, April 17–June 16, 1893. no. 3360, p. 270, Supplement.
Hayward, Jane. "Stained-Glass Windows from the Carmelite Church at Boppard-am-Rhein: A Reconstruction of the Glazing Program of the North Nave." Metropolitan Museum Journal 2 (1969). pp. 82–85, fig. 7.
Caviness, Madeline H., ed. Stained Glass Before 1700 in American Collections: New England and New York (Corpus Vitrearum Checklist I). Studies in the History of Art, Vol. 15. Washington, D.C.: National Art Gallery, 1985. p. 120.
The Met Collection API is where all makers, creators, researchers, and dreamers can now connect to the most up-to-date data and images for more than 470,000 artworks in The Met collection. As part of The Met’s Open Access program, the data is available for unrestricted commercial and noncommercial use without permission or fee.
Displaying stained glass in a museum
Senior Stained Glass Conservator
Stained glass is considered to be one of the more difficult objects to display in a museum, not because it needs strict environmental conditions but because it involves far more than placing it inside a case, hanging it on a wall or moving it into the correct position on the floor. The majority of the stained glass panels in the V&A's collection were originally part of a building's architecture and as such they can be large and heavy. It is not unusual for one object to consist of multiple panels that need to be supported individually. Artificially lighting stained glass at a suitable level provides a further challenge for designers because stained glass was designed to be illuminated by natural light, which changes throughout the day as well as the seasons.
Since the mid-1980s, the V&A's stained glass objects have been mounted in handmade L-section frames constructed from light aluminium alloy and painted black using a low-gloss polyester powder coating before going on display at the Museum or in external venues. The Stained Glass Conservation Studio devised these frames to protect and support the panels during installation, display, storage and transport. Their use also provides consistency for gallery and exhibition designers and enables appropriately trained technicians and curators to handle the panels safely and confidently without always requiring the presence of a stained glass conservator.
Figure 1. False wall display in the Whiteley Sacred Silver & Stained Glass Galleries (Photography by V&A Photographic Studio) (click image for larger version)
After a stained glass panel has been placed in its frame, a piece of clear Perspex® or Makrolon® is placed directly behind it to provide added support. The stained glass panel and its backing sheet are held in place with L-section brackets and screws so the frames can be removed easily without causing any stress or damage to the objects. The construction of the frame also allows for an additional piece of Perspex/Makrolon to be placed in front of the panel, which is necessary when it is displayed at a low level without a physical barrier. For irregularly-shaped panels, thin black aluminium infills are fitted under the flanges of the perimeter leads to fill the spaces between the stained glass and the rectangular frame.
False walls are often constructed for displaying stained glass in temporary exhibitions and permanent galleries. Ideally a false wall will be built far enough out from the existing gallery wall to allow the stained glass to be installed from behind it. Apertures with rebates corresponding to the dimensions of each framed stained glass panel are cut into the false wall. The framed panels are placed into their apertures from behind the false wall and held in place with wooden beading.
Figure 2. Wall-hung lightbox in the entrance of the Whiteley Sacred Silver & Stained Glass Galleries (Photography by V&A Photographic Studio) (click image for larger version)
In galleries where space is limited, like the long, narrow Whiteley Sacred Silver & Stained Glass Galleries, the false wall construction can only be deep enough to accommodate the required services and light fixtures (Figure 1). In these cases, the rebate is reversed so that the panels can be installed from the front of the false wall. Instead of using beading, a fascia board or decorative masking frame is fitted to the front of the aperture to hold the panels in the rebates. If only a few stained glass panels are to be displayed in one space, designing individual wall-hung lightboxes may be a more desirable alternative to constructing a false wall (Figure 2).
Displaying stained glass on the window side of the Whiteley Sacred Silver & Stained Glass Galleries, which overlook the John Madejski Garden, required a different solution to ensure that visitors could enjoy the views of the re-landscaped garden from these windows. A series of nine 4 metre high metal screens were designed to hold the stained glass while taking advantage of the natural light to illuminate the panels (Figure 3). The design of these screens also enabled some panels to be displayed at eye level, giving visitors the opportunity to engage with these objects at close range.
Stained glass can be illuminated artificially using either a conventional back lighting system or a slim profile edge lighting system. Variations of both were used to enhance the four different display methods chosen for the stained glass in the Whiteley Sacred Silver & Stained Glass Galleries. The stained glass panels displayed along the wall side of the gallery are backlit using fluorescent lamps. The panels displayed in the screens are individually illuminated by LED modules that switch on whenever the natural light coming through the windows needs to be boosted. An edge-lighting system using slimline fluorescent lamps was devised for the wall-hung lightboxes to enable them to be as thin as possible. Finally, the stained glass panel in the display case is edge-lit using fibre optic lighting, which is particularly good for use in enclosed spaces since it does not produce heat.
Following are some basic guidelines for artificially lighting stained glass:
Figure 3. Free-standing screens in the Whiteley Sacred Silver & Stained Glass Galleries (Photography by V&A Photographic Studio) (click image for larger version)
stained glass should not be lit too brightly
the light must be evenly distributed across the entire panel
the diffuser material should not have a distracting pattern that can be seen through clear, unpainted glass
the inside of the lightbox should be painted white to reflect the light source
the light source should generate a minimal amount of heat
suitable ventilation must be provided to dissipate heat
it should be possible to replace faulty lamps or transformers without having to remove the stained glass
the ambient light levels in the gallery should be taken into consideration to ensure too much reflected light does not fall on the stained glass
The new Medieval and Renaissance galleries, due to open in late 2009, will include over 130 stained glass objects amongst its permanent displays. The same basic display and lighting methods will be used, i.e. wall-mounted lightboxes and free-standing support structures, but no doubt with exciting new technology. Regardless of how a museum ultimately chooses to display its stained glass, the most important thing to remember is that the most successful displays will result from involving designers, engineers, conservators, curators, technicians and lighting specialists from the earliest stages of design.
Panels stained glass
Go Glass Project Overlay Stained Glass utilises modern day technology with centuries old craftsmanship to manufacture bespoke coloured leaded glass panels. This popular and versatile process uses overlay stained glass colours and leaded strip to one side of the glass which means that it can be double glazed, toughened and even supplied in products such as fire retention glasses.
One advantage of the overlay method is that you can combine an almost limitless range of colours with textures and effects such as marbled colours. This can allow for a completely bespoke and unique range of glass designs, Using glasses such as “Flemish and minster” effects also allows you to create an aged look and designs capturing the art deco and nouveau effects are very current in todays interior design.
Coloured glass can reflect light and colour around your walls and you can create stunning effects when used with edge lighting or incorporate etched glass also into your design.
Energy saving, project overlay stained glass can also be incorporated into a double glazing unit so that you can use the glass panels in doors and windows, create a stunning entranceway into your home with contemporary or traditional designs.
The Go Glass design team will work with you to create your unique glass design, why not visit our showroom in Cambridge and see our craftsmen at work? There are a range of designs to choose from and a bespoke design service simply send us your ideas as a sketch, photo or simply a description and allow us to design something unique to you for your frameless glass door or partition. Our glass artist and Design Director has worked for over 30 years at Go Glass Design and welcomes a challenge, he has exhibited around Europe and enjoys projects both large and small for retail or commercial clients.
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the 2021 china international service trade fair (service trade fair) will be held in beijing from september 2nd to 7th. meanwhile, the global service trade summit will be held on september 2. president xi jinping will deliver a speech at the global service trade summit via video.
as one of the three major exhibition platforms for china's opening to the outside world, the service trade fair has become a leading event in the field of global service trade, and is a close link between china and the world. people from many countries and the media expressed that they look forward to the 2021 service trade fair that will continue to provide opportunities for all parties to deepen cooperation, build consensus, and promote global economic recovery in the post-epidemic era.
"service trade fair has become an important global platform"
this year, the service trade fair will host 5 summit forums, 193 forum meetings and promotion and negotiation activities, as well as 8 side events. more than 10,000 companies from 153 countries and regions have registered to participate in the exhibition, and the world's top 500 and industry-leading companies accounted for 18%, an increase of 9 percentage points from the previous time. the heads of exhibitors and enterprises said that the increase in the attractiveness of the service trade fair stems from china's open cooperation environment and broad development prospects.
tang zhimin, director of the china-asean studies center of the chia university school of management in thailand, said that this year's service trade fair will cover all major areas of service trade, build a platform and provide opportunities for international service trade cooperation, and will inject impetus into the development of global service trade.
"during the service trade fair in 2020, we participated in the winter sports special exhibition, and the response was very good." thomas tajuman, general manager of the czech ski brand alpine china market, said that many european brands have gained more cooperation opportunities through the service trade fair. . "as the beijing winter olympics approach, china's ice and snow sports market will usher in rapid growth. this is a good development opportunity for us."
zvi schiller, chairman of the israel robotics association, said that many professionals and investors are expected to participate in this service trade fair. china has a huge market and strong manufacturing capabilities, and the association is considering establishing a joint r&d center with china.
the panamanian "star" published an article that panama regards the service trade fair as an important boost to the global economic recovery in the post-epidemic era. mark garcia, senior regional consultant of lixin certified public accountants in panama business consulting company, believes that the trade in service is an excellent opportunity to promote cooperation between panama and china in the field of digital economy services. "the service trade fair can allow foreign investors to better understand china, as well as the service trade support and facilitation measures china provides, which will further enhance investors' confidence in long-term investment in china."
"china has become a major trading partner of many countries. the holding of the service trade fair not only conveys to the world china's confidence in opening up to the outside world, but also promotes trade exchanges between china and other economies and builds an important platform for exchanges and cooperation. "brazil business leaders organization china chairman everton monezi said.
wesley douglas, director of the african carbon exchange, is very pleased to see that this year's service trade will include carbon peaking and carbon neutrality as a key issue. “the service trade fair has become an important global platform, and this platform is helpful for solving global problems.” he said that china has provided an important reference for developing countries to practice green development, and african countries have a strong desire for green economic development. , there is an urgent need for related investment and technology introduction. africa and china have great potential for cooperation in these areas.
"digital technology brings hope to the future"
in his speech at the 2020 service trade conference global service trade summit, president xi jinping emphasized that it is necessary to comply with the development trend of digitalization, networking, and intelligence, and work together to eliminate the "digital divide" and promote the digitalization of service trade. the theme of this year's service trade fair is "digital opens up the future, service promotes development". visitors will experience various innovative service products and the latest technologies provided by domestic and foreign enterprises through the service trade fair. in particular, new services centered on the digital economy have received widespread attention from the international community.
yukio kajida, a professor at chuo university in japan, said that in the post-epidemic era, the importance of the digital economy has become more and more prominent. governments and enterprises of various countries are actively promoting the development of the digital economy, and china is at the forefront of this field. this year's service trade fair uses "digitalization" as a key word, which will help promote cooperation and exchanges between global companies in the new situation, and further contribute to global technological innovation, economic development and improvement of people's lives. trade in services will become an important force to promote the recovery of the world economy.
everton monezi said that china’s experience in promoting the application of electronic payment technology is worth learning from latin america. latin american countries are starting to revitalize their economies in order to achieve long-term sustainable development. the service trade fair provides a high-level platform for cooperation between latin america and china, allowing more high-quality latin american companies to enter the chinese market and contribute to the recovery of the world economy.
"digital technology brings hope to the future." susanna gutkovska, acting chief representative of the beijing office of the polish national tourism administration, said that this year's "cloud showroom" at the service trade fair provided them with the opportunity to contact and communicate with their chinese partners. an opportunity for chinese tourists to issue invitations. poland's primorsky province and warsaw tourism organization set up booths in the yunshang exhibition hall to attract visitors. the holding of the service trade fair will help the recovery of the global tourism industry.
karl fei, a professor at the business school of aalto university in finland, believes that china has accumulated a lot of experience in the development of the digital economy. for example, the government provides policy support for enterprises, revitalizes the domestic market for digital services, and supports and encourages innovative companies in this field. share and discuss these experiences with all parties at the service trade conference.
"it is of great significance to the recovery of the world economy"
according to data from the ministry of commerce of china, despite the impact of the epidemic, china's total service imports and exports in 2020 will still exceed rmb 4.5 trillion. in the first half of this year, the added value of china's service industry reached 29.6 trillion yuan, accounting for 55.7% of gdp, providing strong support for the high-quality development of service trade. international sources said that under the background of economic globalization, china's economy is open and inclusive, opening its doors to embrace companies from all over the world, and will contribute wisdom and strength to the deepening of global service trade and investment cooperation.
autumn winter autumn and winter Stained Glass Panels， Mid 20th Century Mouth Blown， unframed - Squares savingsas the guest country of this year's service and trade fair, ireland has not only set up exhibition areas for investment, food, health, education, etc., it will also show the unique charm of ireland through ethnic dance performances and movies. four institutions including the irish food board, the trade and technology board, the investment development board, and the tourism board will appear together on the stage of the service trade fair for the first time. fenbar cleary, vice president of the irish-china science and technology exchange association, said that china's total service trade imports may reach us$10 trillion in the next 15 years, which contains huge market opportunities.
mohamed farahart, director of the egyptian pyramid politics and strategic research center, said that the service and trade will build a sound framework for international cooperation, create a healthier business and investment environment, help establish a new operating structure and trade network, and promote service trade. , investment and capital flow.
lu yaoqun, director of the institute of governance and sustainable development of the national university of singapore business school, said that the service trade association is an excellent platform to promote the development of free trade and common prosperity between china, asia and the rest of the world. the service trade association once again confirmed china's long-term commitment to the idea of building a community with a shared future for mankind.
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tang zhimin said that open and inclusive service trade is also an important part of the regional comprehensive economic partnership agreement. china has used practical actions to create an open and inclusive environment for cooperation through the holding of service trade fairs and china international import expo. "under the current economic situation, china insists on expanding its opening up to the outside world and leading global cooperation. these measures are of great significance to the recovery of the world economy."
hanat besek, president of the china association for the promotion of trade in kazakhstan, said that china’s opening to the outside world has evolved from the initial policy preferences to the current institutional opening, which not only benefits the chinese people, but also contributes to the economic development of neighboring countries. significant driving effect.
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Coloured glass and the works that are made from it
For other uses, see Stained glass (disambiguation).
The term stained glass refers to coloured glass as a material and to works created from it. Throughout its thousand-year history, the term has been applied almost exclusively to the windows of churches and other significant religious buildings. Although traditionally made in flat panels and used as windows, the creations of modern stained glass artists also include three-dimensional structures and sculpture. Modern vernacular usage has often extended the term "stained glass" to include domestic lead light and objets d'art created from foil glasswork exemplified in the famous lamps of Louis Comfort Tiffany.
As a material stained glass is glass that has been coloured by adding metallic salts during its manufacture, and usually then further decorating it in various ways. The coloured glass is crafted into stained glass windows in which small pieces of glass are arranged to form patterns or pictures, held together (traditionally) by strips of lead and supported by a rigid frame. Painted details and yellow stain are often used to enhance the design. The term stained glass is also applied to windows in enamelled glass in which the colours have been painted onto the glass and then fused to the glass in a kiln; very often this technique is only applied to parts of a window.
Stained glass, as an art and a craft, requires the artistic skill to conceive an appropriate and workable design, and the engineering skills to assemble the piece. A window must fit snugly into the space for which it is made, must resist wind and rain, and also, especially in the larger windows, must support its own weight. Many large windows have withstood the test of time and remained substantially intact since the Late Middle Ages. In Western Europe, together with illuminated manuscripts, they constitute the major form of medieval pictorial art to have survived. In this context, the purpose of a stained glass window is not to allow those within a building to see the world outside or even primarily to admit light but rather to control it. For this reason stained glass windows have been described as "illuminated wall decorations".
The design of a window may be abstract or figurative; may incorporate narratives drawn from the Bible, history, or literature; may represent saints or patrons, or use symbolic motifs, in particular armorial. Windows within a building may be thematic, for example: within a church – episodes from the life of Christ; within a parliament building – shields of the constituencies; within a college hall – figures representing the arts and sciences; or within a home – flora, fauna, or landscape.
During the late medieval period, glass factories were set up where there was a ready supply of silica, the essential material for glass manufacture. Silica requires a very high temperature to melt, something not all glass factories were able to achieve. Such materials as potash, soda, and lead can be added to lower the melting temperature. Other substances, such as lime, are added to rebuild the weakened network and make the glass more stable. Glass is coloured by adding metallic oxide powders or finely divided metals while it is in a molten state. Copper oxides produce green or bluish green, cobalt makes deep blue, and gold produces wine red and violet glass. Much of modern red glass is produced using copper, which is less expensive than gold and gives a brighter, more vermilion shade of red. Glass coloured while in the clay pot in the furnace is known as pot metal glass, as opposed to flashed glass.
Cylinder glass or Muff
Using a blow-pipe, a "gather" (glob) of molten glass is taken from the pot heating in the furnace. The gather is formed to the correct shape and a bubble of air blown into it. Using metal tools, molds of wood that have been soaking in water, and gravity, the gather is manipulated to form a long, cylindrical shape. As it cools, it is reheated so that the manipulation can continue. During the process, the bottom of the cylinder is removed. Once brought to the desired size it is left to cool. One side of the cylinder is opened. It is put into another oven to quickly heat and flatten it, and then placed in an annealer to cool at a controlled rate, making the material more stable. "Hand-blown" cylinder (also called muff glass) and crown glass were the types used in ancient stained-glass windows. Stained glass windows were normally in churches and chapels as well as many more well respected buildings.
This hand-blown glass is created by blowing a bubble of air into a gather of molten glass and then spinning it, either by hand or on a table that revolves rapidly like a potter's wheel. The centrifugal force causes the molten bubble to open up and flatten. It can then be cut into small sheets. Glass formed this way can be either coloured and used for stained-glass windows, or uncoloured as seen in small paned windows in 16th- and 17th-century houses. Concentric, curving waves are characteristic of the process. The centre of each piece of glass, known as the "bull's-eye", is subject to less acceleration during spinning, so it remains thicker than the rest of the sheet. It also has the pontil mark, a distinctive lump of glass left by the "pontil" rod, which holds the glass as it is spun out. This lumpy, refractive quality means the bulls-eyes are less transparent, but they have still been used for windows, both domestic and ecclesiastical. Crown glass is still made today, but not on a large scale.
Rolled glass (sometimes called "table glass") is produced by pouring molten glass onto a metal or graphite table and immediately rolling it into a sheet using a large metal cylinder, similar to rolling out a pie crust. The rolling can be done by hand or by machine. Glass can be "double rolled", which means it is passed through two cylinders at once (similar to the clothes wringers on older washing machines) to yield glass of a specified thickness (typically about 1/8" or 3mm). The glass is then annealed. Rolled glass was first commercially produced around the mid-1830s and is widely used today. It is often called cathedral glass, but this has nothing to do with medieval cathedrals, where the glass used was hand-blown.
Architectural glass must be at least 1/8 of an inch (3 mm) thick to survive the push and pull of typical wind loads. However, in the creation of red glass, the colouring ingredients must be of a certain concentration, or the colour will not develop. This results in a colour so intense that at the thickness of 1/8 inch (3 mm), the red glass transmits little light and appears black. The method employed is to laminate a thin layer of red glass to a thicker body of glass that is clear or lightly tinted, forming "flashed glass".
A lightly coloured molten gather is dipped into a pot of molten red glass, which is then blown into a sheet of laminated glass using either the cylinder (muff) or the crown technique described above. Once this method was found for making red glass, other colours were made this way as well. A great advantage is that the double-layered glass can be engraved or abraded to reveal the clear or tinted glass below. The method allows rich detailing and patterns to be achieved without needing to add more lead-lines, giving artists greater freedom in their designs. A number of artists have embraced the possibilities flashed glass gives them. For instance, 16th-century heraldic windows relied heavily on a variety of flashed colours for their intricate crests and creatures. In the medieval period the glass was abraded; later, hydrofluoric acid was used to remove the flash in a chemical reaction (a very dangerous technique), and in the 19th century sandblasting started to be used for this purpose.
Modern production of traditional glass
There are a number of glass factories, notably in Germany, the United States, England, France, Poland and Russia, which produce high-quality glass, both hand-blown (cylinder, muff, crown) and rolled (cathedral and opalescent). Modern stained-glass artists have a number of resources to use and the work of centuries of other artists from which to learn as they continue the tradition in new ways. In the late 19th and 20th centuries there have been many innovations in techniques and in the types of glass used. Many new types of glass have been developed for use in stained glass windows, in particular Tiffany glass and Dalle de verre.
"Pot metal" and flashed glass
The primary method of including colour in stained glass is to use glass, originally colourless, that has been given colouring by mixing with metal oxides in its melted state (in a crucible or "pot"), producing glass sheets that are coloured all the way through; these are known as "pot metal" glass. A second method, sometimes used in some areas of windows, is flashed glass, a thin coating of coloured glass fused to colourless glass (or coloured glass, to produce a different colour). In medieval glass flashing was especially used for reds, as glass made with gold compounds was very expensive and tended to be too deep in colour to use at full thickness.
Another group of techniques give additional colouring, including lines and shading, by treating the surfaces of the coloured sheets, and often fixing these effects by a light firing in a furnace or kiln. These methods may be used over broad areas, especially with silver stain, which gave better yellows than other methods in the Middle Ages. Alternatively they may be used for painting linear effects, or polychrome areas of detail. The most common method of adding the black linear painting necessary to define stained glass images is the use of what is variously called "glass paint", "vitreous paint", or "grisaille paint". This was applied as a mixture of powdered glass, iron or rust filings to give a black colour, clay, and oil, vinegar or water for a brushable texture, with a binder such as gum arabic. This was painted on the pieces of coloured glass, and then fired to burn away the ingredients giving texture, leaving a layer of the glass and colouring, fused to the main glass piece.
"Silver stain", introduced soon after 1300, produced a wide range of yellow to orange colours; this is the "stain" in the term "stained glass". Silver compounds (notably silver nitrate) are mixed with binding substances, applied to the surface of glass, and then fired in a furnace or kiln. They can produce a range of colours from orange-red to yellow. Used on blue glass they produce greens. The way the glass is heated and cooled can significantly affect the colours produced by these compounds. The chemistry involved is complex and not well understood. The chemicals actually penetrate the glass they are added to a little way, and the technique therefore gives extremely stable results. By the 15th century it had become cheaper than using pot metal glass and was often used with glass paint as the only colour on transparent glass. Silver stain was applied to the opposite face of the glass to silver paint, as the two techniques did not work well one on top of the other. The stain was usually on the exterior face, where it appears to have given the glass some protection against weathering, although this can also be true for paint. They were also probably fired separately, the stain needing a lower heat than the paint.
"Sanguine" or "Cousin's rose"
"Sanguine", "carnation", "Rouge Jean Cousin" or "Cousin's rose", after its supposed inventor, is an iron-based fired paint producing red colours, mainly used to highlight small areas, often on flesh. It was introduced around 1500. Copper stain, similar to silver stain but using copper compounds, also produced reds, and was mainly used in the 18th and 19th centuries.
"Cold paint" is various types of paint that were applied without firing. Contrary to the optimistic claims of the 12th century writer Theophilus Presbyter, cold paint is not very durable, and very little medieval paint has survived.
As well as painting, scratched sgraffito techniques were often used. This involved painting a colour over pot metal glass of another colour, and then before firing selectively scratching the glass paint away to make the design, or the lettering of an inscription. This was the most common method of making inscriptions in early medieval glass, giving white or light letters on a black background, with later inscriptions more often using black painted letters on a transparent glass background.
"Pot glass" colours
These are the colours in which the glass itself is made, as opposed to colours applied to the glass.
Ordinary soda-lime glass appears colourless to the naked eye when it is thin, although iron oxide impurities produce a green tint which becomes evident in thick pieces or with the aid of scientific instruments. A number of additives are used to reduce the green tint, particularly if the glass is to be used for plain window glass, rather than stained glass windows. These additives include manganese dioxide which produces sodium permanganate, and may result in a slightly mauve tint, characteristic of the glass in older houses in New England. Selenium has been used for the same purpose.
While very pale green is the typical colour of transparent glass, deeper greens can be achieved by the addition of Iron(II) oxide which results in a bluish-green glass. Together with chromium it gives glass of a richer green colour, typical of the glass used to make wine bottles. The addition of chromium yields dark green glass, suitable for flashed glass. Together with tin oxide[clarification needed] and arsenic it yields emerald green glass.
- Metallic gold, in very low concentrations (around 0.001%), produces a rich ruby-coloured glass ("ruby gold"); in even lower concentrations it produces a less intense red, often marketed as "cranberry glass". The colour is caused by the size and dispersion of gold particles. Ruby gold glass is usually made of lead glass with tin added.
- Pure metallic copper produces a very dark red, opaque glass. Glass created in this manner is generally "flashed" (laminated glass). It was used extensively in the late 19th and early 20th centuries and exploited for the decorative effects that could be achieved by sanding and engraving.
- Selenium is an important agent to make pink and red glass. When used together with cadmium sulphide, it yields a brilliant red colour known as "Selenium Ruby".
- This was very often achieved by "silver stain" applied externally to the sheets of glass (see above).
- The addition of sulphur, together with carbon and iron salts, is used to form iron polysulphides and produce amber glass ranging from yellowish to almost black. With calcium it yields a deep yellow colour.
- Adding titanium produces yellowish-brown glass. Titanium is rarely used on its own and is more often employed to intensify and brighten other additives.
- Cadmium together with sulphur results in deep yellow colour, often used in glazes. However, cadmium is toxic.
- Uranium (0.1% to 2%) can be added to give glass a fluorescent yellow or green colour.Uranium glass is typically not radioactive enough to be dangerous, but if ground into a powder, such as by polishing with sandpaper, and inhaled, it can be carcinogenic. When used with lead glass with a very high proportion of lead, it produces a deep red colour.
- The addition of manganese gives an amethyst colour. Manganese is one of the oldest glass additives, and purple manganese glass has been used since early Egyptian history.
- Nickel, depending on the concentration, produces blue, or violet, or even black glass.Lead crystal with added nickel acquires a purplish colour.
13th-century window from Chartres showing extensive use of the ubiquitous cobalt blue with green and purple-brown glass, details of amber and borders of flashed red glass.
A 19th-century window illustrates the range of colours common in both Medieval and Gothic Revival glass, Lucien Begule, Lyon (1896)
A 16th-century window by Arnold of Nijmegen showing the combination of painted glass and intense colour common in Renaissance windows
A late 20th-century window showing a graded range of colours. Ronald Whiting, Chapel Studios. Tattershall Castle, UK
A window by Tiffany illustrating the development and use of multi-coloured flashed, opalised and streaky glasses at the end of the 19th century
Creating stained-glass windows
The first stage in the production of a window is to make, or acquire from the architect or owners of the building, an accurate template of the window opening that the glass is to fit.
The subject matter of the window is determined to suit the location, a particular theme, or the wishes of the patron. A small design called a Vidimus (from Latin "we have seen") is prepared which can be shown to the patron. A scaled model maquette may also be provided. The designer must take into account the design, the structure of the window, the nature and size of the glass available and his or her own preferred technique.
A traditional narrative window has panels which relate a story. A figurative window could have rows of saints or dignitaries. Scriptural texts or mottoes are sometimes included and perhaps the names of the patrons or the person to whose memory the window is dedicated. In a window of a traditional type, it is usually left to the discretion of the designer to fill the surrounding areas with borders, floral motifs and canopies.
A full-sized cartoon is drawn for every "light" (opening) of the window. A small church window might typically have two lights, with some simple tracery lights above. A large window might have four or five lights. The east or west window of a large cathedral might have seven lights in three tiers, with elaborate tracery. In medieval times the cartoon was drawn directly on the surface of a whitewashed table, which was then used as a pattern for cutting, painting and assembling the window. The cartoon is then divided into a patchwork, providing a template for each small glass piece. The exact position of the lead which holds the glass in place is also noted, as it is part of the calculated visual effect.
Selecting and painting the glass
Each piece of glass is selected for the desired colour and cut to match a section of the template. An exact fit is ensured by "grozing" the edges with a tool which can nibble off small pieces. Details of faces, hair and hands can be painted onto the inner surface of the glass using a special glass paint which contains finely ground lead or copper filings, ground glass, gum arabic and a medium such as wine, vinegar or (traditionally) urine. The art of painting details became increasingly elaborate and reached its height in the early 20th century.
From 1300 onwards, artists started using "silver stain" which was made with silver nitrate. It gave a yellow effect ranging from pale lemon to deep orange. It was usually painted onto the outside of a piece of glass, then fired to make it permanent. This yellow was particularly useful for enhancing borders, canopies and haloes, and turning blue glass into green glass. By about 1450, a stain known as "Cousin's rose" was used to enhance flesh tones.
In the 16th century, a range of glass stains were introduced, most of them coloured by ground glass particles. They were a form of enamelled glass. Painting on glass with these stains was initially used for small heraldic designs and other details. By the 17th century a style of stained glass had evolved that was no longer dependent upon the skilful cutting of coloured glass into sections. Scenes were painted onto glass panels of square format, like tiles. The colours were then annealed to the glass before the pieces were assembled.
A method used for embellishment and gilding is the decoration of one side of each of two pieces of thin glass, which are then placed back to back within the lead came. This allows for the use of techniques such as Angel gilding and Eglomise to produce an effect visible from both sides but not exposing the decorated surface to the atmosphere or mechanical damage.
Assembly and mounting
Once the glass is cut and painted, the pieces are assembled by slotting them into H-sectioned lead cames. All the joints are then soldered together and the glass pieces are prevented from rattling and the window made weatherproof by forcing a soft oily cement or mastic between the glass and the cames. In modern windows, copper foil is now sometimes used instead of lead. For further technical details, see Came glasswork.
Traditionally, when a window was inserted into the window space, iron rods were put across it at various points to support its weight. The window was tied to these rods with copper wire. Some very large early Gothic windows are divided into sections by heavy metal frames called ferramenta. This method of support was also favoured for large, usually painted, windows of the Baroque period.
- Technical details
Thomas Becket window from Canterbury showing the pot metal and painted glass, lead H-sectioned cames, modern steel rods and copper wire attachments
Detail from a 19th or 20th-century window in Eyneburg, Belgium, showing detailed polychrome painting of face.
Coloured glass has been produced since ancient times. Both the Egyptians and the Romans excelled at the manufacture of small colored glass objects. Phoenicia was important in glass manufacture with its chief centres Sidon, Tyre and Antioch. The British Museum holds two of the finest Roman pieces, the Lycurgus Cup, which is a murky mustard color but glows purple-red to transmitted light, and the cameo glassPortland vase which is midnight blue, with a carved white overlay.
In early Christian churches of the 4th and 5th centuries, there are many remaining windows which are filled with ornate patterns of thinly-sliced alabaster set into wooden frames, giving a stained-glass like effect.
Evidence of stained-glass windows in churches and monasteries in Britain can be found as early as the 7th century. The earliest known reference dates from 675 AD when Benedict Biscop imported workmen from France to glaze the windows of the monastery of St Peter which he was building at Monkwearmouth. Hundreds of pieces of coloured glass and lead, dating back to the late 7th century, have been discovered here and at Jarrow.
In the Middle East, the glass industry of Syria continued during the Islamic period with major centres of manufacture at Raqqa, Aleppo and Damascus and the most important products being highly transparent colourless glass and gilded glass, rather than coloured glass.
In Southwest Asia
The creation of stained glass in Southwest Asia began in ancient times. One of the region's earliest surviving formulations for the production of colored glass comes from the Assyrian city of Nineveh, dating to the seventh century BC. The Kitab al-Durra al-Maknuna, attributed to the 8th century alchemistJābir ibn Hayyān, discusses the production of colored glass in ancient Babylon and Egypt. The Kitab al-Durra al-Maknuna also describes how to create colored glass and artificial gemstones made from high-quality stained glass. The tradition of stained glass manufacture has continued, with mosques, palaces, and public spaces being decorated with stained glass throughout the Islamic world. The stained glass of Islam is generally non-pictorial and of purely geometric design, but may contain both floral motifs and text.
Extensive stained glasses of Nasir-ol-Molk Mosque in Shiraz, Iran and the light passing through them
Stained glass in Dowlat Abad Garden at Yazd, Iran
From a mosque in Jerusalem, this window contains highly detailed text.
Medieval glass in Europe
See also: Poor Man's Bible and Medieval stained glass
Stained glass, as an art form, reached its height in the Middle Ages when it became a major pictorial form used to illustrate the narratives of the Bible to a largely illiterate populace.
In the Romanesque and Early Gothic period, from about 950 to 1240, the untraceried windows demanded large expanses of glass which of necessity were supported by robust iron frames, such as may be seen at Chartres Cathedral and at the eastern end of Canterbury Cathedral. As Gothic architecture developed into a more ornate form, windows grew larger, affording greater illumination to the interiors, but were divided into sections by vertical shafts and tracery of stone. This elaboration of form reached its height of complexity in the Flamboyant style in Europe, and windows grew still larger with the development of the Perpendicular style in England and Rayonnant style in France.
Integrated with the lofty verticals of Gothic cathedrals and parish churches, glass designs became more daring. The circular form, or rose window, developed in France from relatively simple windows with openings pierced through slabs of thin stone to wheel windows, as exemplified by the west front of Chartres Cathedral, and ultimately to designs of enormous complexity, the tracery being drafted from hundreds of different points, such as those at Sainte-Chapelle, Paris and the "Bishop's Eye" at Lincoln Cathedral.
While stained glass was widely manufactured, Chartres was the greatest centre of stained glass manufacture, producing glass of unrivalled quality.
- Medieval glass in Germany and Austria
King David from Augsburg Cathedral, early 12th century. One of the oldest examples in situ.
Crucifixion with Ss Catherine, George and Margaret, Leechkirche, Graz, Austria
The Crucifixion and Virgin and Child in Majesty, Cologne Cathedral, (1340)
- Medieval glass in Spain
Renaissance, Reformation and Classical windows
Probably the earliest scheme of stained glass windows that was created during the Renaissance was that for Florence Cathedral, devised by Lorenzo Ghiberti. The scheme includes three ocular windows for the dome and three for the facade which were designed from 1405 to 1445 by several of the most renowned artists of this period: Ghiberti, Donatello, Uccello and Andrea del Castagno. Each major ocular window contains a single picture drawn from the Life of Christ or the Life of the Virgin Mary, surrounded by a wide floral border, with two smaller facade windows by Ghiberti showing the martyred deacons, St Stephen and St Lawrence. One of the cupola windows has since been lost, and that by Donatello has lost nearly all of its painted details.
In Europe, stained glass continued to be produced; the style evolved from the Gothic to the Classical, which is well represented in Germany, Belgium and the Netherlands, despite the rise of Protestantism. In France, much glass of this period was produced at the Limoges factory, and in Italy at Murano, where stained glass and faceted lead crystal are often coupled together in the same window. The French Revolution brought about the neglect or destruction of many windows in France.
At the Reformation in England, large numbers of medieval and Renaissance windows were smashed and replaced with plain glass. The Dissolution of the Monasteries under Henry VIII and the injunctions of Thomas Cromwell against "abused images" (the object of veneration) resulted in the loss of thousands of windows. Few remain undamaged; of these the windows in the private chapel at Hengrave Hall in Suffolk are among the finest. With the latter wave of destruction the traditional methods of working with stained glass died, and were not rediscovered in England until the early 19th century. See Stained glass – British glass, 1811–1918 for more details.
In the Netherlands a rare scheme of glass has remained intact at Grote Sint-Jan Church, Gouda. The windows, some of which are 18 metres (59 feet) high, date from 1555 to the early 1600s; the earliest is the work of Dirck Crabeth and his brother Wouter. Many of the original cartoons still exist.
The Triumph of Freedom of Conscience, Sint Janskerk, maker Adriaen Gerritszoon de Vrije (Gouda); design Joachim Wtewael (Utrecht) (1595–1600)
Domestic window by Dirck Crabeth for the house of Adriaen Dircxzoon van Crimpen of Leiden. (1543) The windows show scenes from the lives of the Prophet Samuel and the Apostle Paul. Musée des Arts Décoratifs, Paris.
Glass painting depicting Mordnacht (murder night) on 23/24 February 1350 and heraldry of the first Meisen guild's Zunfthaus, Zürich. (c. 1650)
Auch Cathedral (France), Renaissance stained glass by Arnaud de Moles (detail), 1507–1513).
Revival in Britain
Main article: British and Irish stained glass (1811–1918)
The Catholic revival in England, gaining force in the early 19th century with its renewed interest in the medieval church, brought a revival of church building in the Gothic style, claimed by John Ruskin to be "the true Catholic style". The architectural movement was led by Augustus Welby Pugin. Many new churches were planted in large towns and many old churches were restored. This brought about a great demand for the revival of the art of stained glass window making.
Among the earliest 19th-century English manufacturers and designers were William Warrington and John Hardman of Birmingham, whose nephew, John Hardman Powell, had a commercial eye and exhibited works at the Philadelphia Exhibition of 1876, influencing stained glass in the United States of America. Other manufacturers included William Wailes, Ward and Hughes, Clayton and Bell, Heaton, Butler and Bayne and Charles Eamer Kempe. A Scottish designer, Daniel Cottier, opened firms in Australia and the US.
One of England's largest windows, the east window of Lincoln Cathedral, Ward and Nixon (1855), is a formal arrangement of small narrative scenes in roundels
William Wailes. This window has the bright pastel colour, wealth of inventive ornament, and stereotypical gestures of windows by this firm. St Mary's, Chilham
Revival in France
Further information: List of French stained glass manufacturers
In France there was a greater continuity of stained glass production than in England. In the early 19th century most stained glass was made of large panes that were extensively painted and fired, the designs often being copied directly from oil paintings by famous artists. In 1824 the Sèvres porcelain factory began producing stained glass to supply the increasing demand. In France many churches and cathedrals suffered despoliation during the French Revolution. During the 19th century a great number of churches were restored by Viollet-le-Duc. Many of France's finest ancient windows were restored at that time. From 1839 onwards much stained glass was produced that very closely imitated medieval glass, both in the artwork and in the nature of the glass itself. The pioneers were Henri Gèrente and André Lusson. Other glass was designed in a more Classical manner, and characterised by the brilliant cerulean colour of the blue backgrounds (as against the purple-blue of the glass of Chartres) and the use of pink and mauve glass.
Detail of a "Tree of Jesse" window in Reims Cathedral designed in the 13th-century style by L. Steiheil and painted by Coffetier for Viollet-le-Duc, (1861)
St Louis administering Justice by Lobin in the painterly style. (19th century) Church of St Medard, Thouars.
During the mid- to late 19th century, many of Germany's ancient buildings were restored, and some, such as Cologne Cathedral, were completed in the medieval style. There was a great demand for stained glass. The designs for many windows were based directly on the work of famous engravers such as Albrecht Dürer. Original designs often imitate this style. Much 19th-century German glass has large sections of painted detail rather than outlines and details dependent on the lead. The Royal Bavarian Glass Painting Studio was founded by Ludwig I in 1827. A major firm was Mayer of Munich, which commenced glass production in 1860, and is still operating as Franz Mayer of Munich, Inc.. German stained glass found a market across Europe, in America and Australia. Stained glass studios were also founded in Italy and Belgium at this time.
In the Austrian Empire and later Austria-Hungary, one of the leading stained glass artists was Carl Geyling, who founded his studio in 1841. His son would continue the tradition as Carl Geyling's Erben, which still exists today. Carl Geyling's Erben completed numerous stained glass windows for major churches in Vienna and elsewhere, and received an Imperial and Royal Warrant of Appointment from emperor Franz Joseph I of Austria.
Innovations in Britain and Europe
Among the most innovative English designers were the Pre-Raphaelites, William Morris (1834–1898) and Edward Burne-Jones (1833–1898), whose work heralds the influential Arts & Crafts Movement, which regenerated stained glass throughout the English-speaking world. Amongst its most important exponents in England was Christopher Whall (1849-1924), author of the classic craft manual 'Stained Glass Work' (published London and New York, 1905), who advocated the direct involvement of designers in the making of their windows. His masterpiece is the series of windows (1898-1910) in the Lady Chapel at Gloucester Cathedral. Whall taught at London's Royal College of Art and Central School of Arts and Crafts: his many pupils and followers included Karl Parsons, Mary Lowndes, Henry Payne, Caroline Townshend, Veronica Whall (his daughter) and Paul Woodroffe. The Scottish artist Douglas Strachan (1875-1950), who was much influenced by Whall's example, developed the Arts & Crafts idiom in an expressionist manner, in which powerful imagery and meticulous technique are masterfully combined. In Ireland, a generation of young artists taught by Whall's pupil Alfred Child at Dublin's Metropolitan School of Art created a distinctive national school of stained glass: its leading representatives were Wilhelmina Geddes, Michael Healy and Harry Clarke.
Art Nouveau or Belle Epoque stained glass design flourished in France, and Eastern Europe, where it can be identified by the use of curving, sinuous lines in the lead, and swirling motifs. In France it is seen in the work of Francis Chigot of Limoges. In Britain it appears in the refined and formal leadlight designs of Charles Rennie Mackintosh.
David's charge to Solomon shows the strongly linear design and use of flashed glass for which Burne-Jones' designs are famous. Trinity Church, Boston, US, (1882)
God the Creator by Stanisław Wyspiański, this window has no glass painting, but relies entirely on leadlines and skilful placement of colour and tone. Franciscan Church, Kraków (c. 1900)
Art Nouveau by Jacques Grüber, the glass harmonising with the curving architectural forms that surround it, Musée de l'École de Nancy (1904).
Innovations in the United States
Main article: Tiffany glass
J&R Lamb Studios, established in 1857 in New York City, was the first major decorative arts studio in the United States and for many years a major producer of ecclesiastical stained glass.
Notable American practitioners include John La Farge (1835–1910), who invented opalescent glass and for which he received a U.S. patent on 24 February 1880, and Louis Comfort Tiffany (1848–1933), who received several patents for variations of the same opalescent process in November of the same year and he used the copper foil method as an alternative to lead in some windows, lamps and other decorations. Sanford Bray of Boston patented the use of copper foil in stained glass in 1886, However, a reaction against the aesthetics and technique of opalescent windows - led initially by architects such as Ralph Adams Cram - led to a rediscovery of traditional stained glass in the early 1900s. Charles J. Connick (1875-1945), who founded his Boston studio in 1913, was profoundly influenced by his study of medieval stained glass in Europe and by the Arts & Crafts philosophy of Englishman Christopher Whall. Connick created hundreds of windows throughout the US, including major glazing schemes at Princeton University Chapel (1927-9) and at Pittsburgh's Heinz Memorial Chapel (1937-8). Other American artist-makers who espoused a medieval-inspired idiom included Nicola D'Ascenzo of Philadelphia, Wilbur Burnham and Reynolds, Francis & Rohnstock of Boston and Henry Wynd Young and J. Gordon Guthrie of New York.
John La Farge, The Angel of Help, North Easton, MA shows the use of tiny panes contrasting with large areas of opalescent glass. Window restored by Victor Rothman Stained Glass, Yonkers NY
Religion Enthroned, J&R Lamb Studios, designer Frederick Stymetz Lamb, c. 1900. Brooklyn Museum. Symmetrical design, "Aesthetic Style", a limited palette and extensive use of mottled glass.
The Holy City by Louis Comfort Tiffany (1905). This 58-panel window has brilliant red, orange, and yellow etched glass for the sunrise, with textured glass used to create the effect of moving water.
20th and 21st centuries
Many 19th-century firms failed early in the 20th century as the Gothic movement was superseded by newer styles. At the same time there were also some interesting developments where stained glass artists took studios in shared facilities. Examples include the Glass House in London set up by Mary Lowndes and Alfred J. Drury and An Túr Gloine in Dublin, which was run by Sarah Purser and included artists such as Harry Clarke.
A revival occurred in the middle of the century because of a desire to restore thousands of church windows throughout Europe destroyed as a result of World War II bombing. German artists led the way. Much work of the period is mundane and often was not made by its designers, but industrially produced.
Other artists sought to transform an ancient art form into a contemporary one, sometimes using traditional techniques while exploiting the medium of glass in innovative ways and in combination with different materials. The use of slab glass, a technique known as Dalle de Verre, where the glass is set in concrete or epoxy resin, was a 20th-century innovation credited to Jean Gaudin and brought to the UK by Pierre Fourmaintraux. One of the most prolific glass artists using this technique was the Dominican FriarDom Charles Norris OSB of Buckfast Abbey.
Gemmail, a technique developed by the French artist Jean Crotti in 1936 and perfected in the 1950s, is a type of stained glass where adjacent pieces of glass are overlapped without using lead cames to join the pieces, allowing for greater diversity and subtlety of colour. Many famous works by late 19th- and early 20th-century painters, notably Picasso, have been reproduced in gemmail. A major exponent of this technique is the German artist Walter Womacka.
Among the early well-known 20th-century artists who experimented with stained glass as an Abstract art form were Theo van Doesburg and Piet Mondrian. In the 1960s and 1970s the Expressionist painter Marc Chagall produced designs for many stained glass windows that are intensely coloured and crammed with symbolic details. Important 20th-century stained glass artists include John Hayward, Douglas Strachan, Ervin Bossanyi, Louis Davis, Wilhelmina Geddes, Karl Parsons, John Piper, Patrick Reyntiens, Johannes Schreiter, Brian Clarke, Paul Woodroffe, Jean René Bazaine at Saint Séverin, Sergio de Castro at Couvrechef- La Folie (Caen), Hamburg-Dulsberg and Romont (Switzerland), and the Loire Studio of Gabriel Loire at Chartres. The west windows of England's Manchester Cathedral, by Tony Hollaway, are some of the most notable examples of symbolic work.
In Germany, stained glass development continued with the inter-war work of Johan Thorn Prikker and Josef Albers, and the post-war achievements of Joachim Klos, Johannes Schreiter and Ludwig Shaffrath. This group of artists, who advanced the medium through the abandonment of figurative designs and painting on glass in favour of a mix of biomorphic and rigorously geometric abstraction, and the calligraphic non-functional use of leads, are described as having produced "the first authentic school of stained glass since the Middle Ages". The works of Ludwig Schaffrath demonstrate the late 20th-century trends in the use of stained glass for architectural purposes, filling entire walls with coloured and textured glass. In the 1970s young British stained-glass artists such as Brian Clarke were influenced by the large scale and abstraction in German twentieth-century glass.
In the UK, the professional organisation for stained glass artists has been the British Society of Master Glass Painters, founded in 1921. Since 1924 the BSMGP has published an annual journal, The Journal of Stained Glass. It continues to be Britain's only organisation devoted exclusively to the art and craft of stained glass. From the outset, its chief objectives have been to promote and encourage high standards in stained glass painting and staining, to act as a locus for the exchange of information and ideas within the stained glass craft and to preserve the invaluable stained glass heritage of Britain. See www.bsmgp.org.uk for a range of stained glass lectures, conferences, tours, portfolios of recent stained glass commissions by members, and information on courses and the conservation of stained glass. Back issues of The Journal of Stained Glass are listed and there is a searchable index for stained glass articles, an invaluable resource for stained glass researchers.
After the First World War, stained glass window memorials were a popular choice among wealthier families, examples can be found in churches across the UK.
In the United States, there is a 100-year-old trade organization, The Stained Glass Association of America, whose purpose is to function as a publicly recognized organization to assure survival of the craft by offering guidelines, instruction and training to craftspersons. The SGAA also sees its role as defending and protecting its craft against regulations that might restrict its freedom as an architectural art form. The current president is Kathy Bernard. Today there are academic establishments that teach the traditional skills. One of these is Florida State University's Master Craftsman Program, which recently completed a 30 ft (9.1 m) high stained-glass windows, designed by Robert Bischoff, the program's director, and Jo Ann, his wife and installed to overlook Bobby Bowden Field at Doak Campbell Stadium. The Roots of Knowledge installation at Utah Valley University in Orem, Utah is 200 feet (61 m) long and has been compared to those in several European cathedrals, including the Cologne Cathedral in Germany, Sainte-Chapelle in France, and York Minster in England.
Thin slices of agate set into lead and glass, Grossmünster, Zürich, Switzerland, by Sigmar Polke (2009)
Combining ancient and modern traditions
Mid-20th-century window showing a continuation of ancient and 19th-century methods applied to a modern historical subject. Florence Nightingale window at St Peters, Derby, made for the Derbyshire Royal Infirmary
Figurative design using the lead lines and minimal glass paint in the 13th-century manner combined with the texture of Cathedral glass, Ins, Switzerland
St Michael and the Devil at the church of St Michael Paternoster Row, by English artist John Hayward combines traditional methods with a distinctive use of shard-like sections of glass.
Buildings incorporating stained glass windows
Stained glass windows were commonly used in churches for decorative and informative purposes. Many windows are donated to churches by members of the congregation as memorials of loved ones. For more information on the use of stained glass to depict religious subjects, see Poor Man's Bible.
- Important examples
- Cathedral of Chartres, in France, 11th- to 13th-century glass
- Canterbury Cathedral, in England, 12th to 15th century plus 19th- and 20th-century glass
- York Minster, in England, 11th- to 15th-century glass
- Sainte-Chapelle, in Paris, 13th- and 14th-century glass
- Florence Cathedral, Italy, 15th-century glass designed by Uccello, Donatello and Ghiberti
- St. Andrew's Cathedral, Sydney, Australia, early complete cycle of 19th-century glass, Hardman of Birmingham.
- Fribourg Cathedral, Switzerland, complete cycle of glass 1896–1936, by Józef Mehoffer
- Coventry Cathedral, England, mid-20th-century glass by various designers, the large baptistry window being by John Piper
- Brown Memorial Presbyterian Church, extensive collection of windows by Louis Comfort Tiffany
In addition to Christian churches, stained glass windows have been incorporated into Jewish temple architecture for centuries. Jewish communities in the United States saw this emergence in the mid-19th century, with such notable examples as the sanctuary depiction of the Ten Commandments in New York's Congregation Anshi Chesed. From the mid-20th century to the present, stained glass windows have been a ubiquitous feature of American synagogue architecture. Styles and themes for synagogue stained glass artwork are as diverse as their church counterparts. As with churches, synagogue stained glass windows are often dedicated by member families in exchange for major financial contributions to the institution.
Places of worship
Interior of the Blue Mosque, Istanbul.
Stained glass windows in the Mosque of Srinagar, Kashmir
Late 20th-century stained glass from Temple Ohev Sholom, Harrisburg, Pennsylvania by Ascalon Studios.
Mausolea, whether for general community use or for private family use, may employ stained glass as a comforting entry for natural light, for memorialization, or for display of religious imagery.
Stained-glass window in the Benedum mausoleum, Homewood Cemetery, Pittsburgh, Pennsylvania
Stained glass windows in houses were particularly popular in the Victorian era and many domestic examples survive. In their simplest form they typically depict birds and flowers in small panels, often surrounded with machine-made cathedral glass which, despite what the name suggests, is pale-coloured and textured. Some large homes have splendid examples of secular pictorial glass. Many small houses of the 19th and early 20th centuries have leadlight windows.
Public and commercial buildings
Stained glass has often been used as a decorative element in public buildings, initially in places of learning, government or justice but increasingly in other public and commercial places such as banks, retailers and railway stations. Public houses in some countries make extensive use of stained glass and leaded lights to create a comfortable atmosphere and retain privacy.