Historical Stained Glass Windows Research Articles

Evaluation of the Composition, Thermal and Mechanical Behavior, and Color Changes of Artificially and Naturally Aged Polymers for the Conservation of Stained Glass Windows.

Investigations of historical conservation materials on historical stained glass windows of the Naumburg Cathedral in Germany offered an opportunity for the study of polymers, naturally aged in a non-controlled environment. This allowed the conservation history of the cathedral to be traced and expanded by valuable insights. The historical materials were characterized through the use of spectroscopy (FTIR, Raman), thermal analysis, PY-GC/MS, and SEC on taken samples. The analyses show that acrylate resins were predominantly used for conservation. The lamination material from the 1940s is particularly noteworthy. Epoxy resins were also identified in isolated cases. Artificial aging was used to investigate the influence of environmental influences on the properties of the identified materials. Through a multi-stage aging program, influences of UV radiation, high temperatures and high humidity can be considered in isolation. Piaflex F20, Epilox, Paraloid B72 as a modern material and combinations of Paraloid B72/diisobutyl phthalate and PMA/diisobutyl phthalate were investigated. The parameters yellowing, FTIR spectra, Raman spectra, molecular mass and conformation, glass transition temperature, thermal behavior, and adhesive strength on glass were determined. The effects of the environmental parameters on the investigated materials are differentiated. UV and extreme temperatures tend to show a stronger influence than humidity. The comparison of the artificially aged samples with the naturally aged samples from the cathedral shows that the latter were less aged. Recommendations for the conservation of the historical stained glass windows were derived from the results of the investigation.

Eliminating Temporal Illumination Variations in Whisk-broom Hyperspectral Imaging

We propose a method for eliminating the temporal illumination variations in whisk-broom (point-scan) hyperspectral imaging. Whisk-broom scanning is useful for acquiring a spatial measurement using a pixel-based hyperspectral sensor. However, when it is applied to outdoor cultural heritages, temporal illumination variations become an issue due to the lengthy measurement time. As a result, the incoming illumination spectra vary across the measured image locations because different locations are measured at different times. To overcome this problem, in addition to the standard raster scan, we propose an additional perpendicular scan that traverses the raster scan. We show that this additional scan allows us to infer the illumination variations over the raster scan. Furthermore, the sparse structure in the illumination spectrum is exploited to robustly eliminate these variations. We quantitatively show that a hyperspectral image captured under sunlight is indeed affected by temporal illumination variations, that a Naïve mitigation method suffers from severe artifacts, and that the proposed method can robustly eliminate the illumination variations. Finally, we demonstrate the usefulness of the proposed method by capturing historic stained-glass windows of a French cathedral.

3D INSPECTION OF THE RESTORATION AND CONSERVATION OF STAINED GLASS WINDOWS USING HIGH RESOLUTION STRUCTURED LIGHT SCANNING

Abstract. The initial focus of this research was on the development of a general workflow for the documentation and monitoring of historical stained glass windows using structured light scanning. Therefore windows from different churches, time periods and with different corrosion and damage phenomena were scanned before and after conservation measures. To evaluate the execution of the restoration measures the data was compared using 3D inspection software to examine the differences in geometry between the two scans. Various problems had to be solved, for example, how to deal with heavily reflective surfaces and the extreme contrast between light and dark surfaces, as seen in the borders between ‘Schwarzlot’ painting and plain glass. The application of materials for matting the surfaces, such as Cyclododecane spray, was impossible due to the high accuracy of the surface measurement required for 3D inspection. Regarding the contrast differences of the surfaces, the creation of exposure fusions and the use of polarization filters to reduce reflections were tested. In addition to the general problems encountered when recording translucent surfaces, the historical glasses caused additional problems in calculating surface comparisons. For example, the windows have to be moved and turned around several times, both during the conservation process and while scanning, causing deformations of the geometry due to the flexible lead rods allowing a certain degree of movement.

Early stages of glass alteration in the coastal atmosphere

Urban and industrial atmospheres can produce several damages on glass façades and historical stained-glass windows; however, the effect of coastal atmosphere on them has been scarcely studied. This work presents the results of the exposure of soda-lime, potash-lime, and mixed-alkali silicate glass to the coastal atmosphere in Cape Vilán (Galicia, Spain) at different distances to the coast (inland) during twelve months. Crystalline deposits were observed on all the samples, although their quantity depended on the meteorological conditions. The samples located nearest to the coast presented alteration layers, while those ones located farthest from the shore presented several isolated pits. Regarding the chemical composition, potash-lime silicate glass, typical composition from medieval glass windows, was the most altered glass in contrast to soda-lime and mixed-alkali silicate glasses.

Application of sol-gel based sensors to environmental monitoring of Mauméjean stained glass windows housed in two different buildings at downtown Madrid

Degradation of historical stained glass windows is mainly caused by acid attack enhanced by humidity and pollutants. Accordingly, their preventive conservation should include environmental evaluation. Maumejean�s stained glass windows (c 1940) of two buildings located at downtown Madrid have been monitored by sol-gel sensors of acidity and temperature. The philosophy was the application of innovative glassy sol-gel sensors to assess the conservation conditions of stained glass windows, i.e. modern materials for preservation of historical materials. Conservation conditions (environmental acidity and temperature) of restored and non-restored stained glass windows have been recorded throughout 13 months. The main contributing parameter to outdoor acidity is proximity to road traffic, which produces acid species able to diminish two units of pH with respect to neutral conditions. This acid environment affects both sides of stained glass windows, even in those protected with a glazing system, which allows natural ventilation. Other contributing parameters to increase the air acidity were facade orientation, sensor position, distance to pollutants sources, human interaction and uncontrolled ventilation.

Evaluation of manganese-bodies removal in historical stained glass windows via SR-μ-XANES/XRF and SR-μ-CT

The speed and effectiveness of a conservation treatment used for stained glass windows have been investigated. Dark-coloured Mn-rich stains can be found in the alteration layer of ancient glass artefacts and cause the surface to turn brown/black: this phenomenon is known as Mn-browning or Mn-staining. While in glass manganese is present in the +II or +III oxidation states, in the Mn-rich bodies, manganese is in a higher oxidation state (+IV). In restoration practice, mildly reducing solutions are employed to eliminate the dark colour and restore the clear appearance of the glass. In this paper the effectiveness and side effects of the use of hydroxylamine hydrochloride for this purpose are assessed. Archaeological fragments of stained glass windows, dated to the 14th century and originating from Sidney Sussex College, Cambridge (UK), were examined by means of synchrotron radiation (SR) based microscopic X-ray Absorption Near-Edge Spectroscopy (μ-XANES) and microscopic X-Ray Fluorescence (μ-XRF) and with high resolution computed absorption tomography (μ-CT) before, during and after the treatment. The monitoring of the glass fragments during the treatment allows us to better understand the manner in which the process unfolds and its kinetics. The results obtained reveal that the hydroxylamine hydrochloride treatment is effective, but also that it has a number of unwanted side effects. These findings are useful for optimizing the time and other modalities of the Mn-reducing treatment as well as minimizing its unwanted results.

A three-step unsupervised neural model for visualizing high complex dimensional spectroscopic data sets

The interdisciplinary research presented in this study is based on a novel approach to clustering tasks and the visualization of the internal structure of high-dimensional data sets. Following normalization, a pre-processing step performs dimensionality reduction on a high-dimensional data set, using an unsupervised neural architecture known as cooperative maximum likelihood Hebbian learning (CMLHL), which is characterized by its capability to preserve a degree of global ordering in the data. Subsequently, the self organising-map (SOM) is applied, as a topology-preserving architecture used for two-dimensional visualization of the internal structure of such data sets. This research studies the joint performance of these two neural models and their capability to preserve some global ordering. Their effectiveness is demonstrated through a case of study on a real-life high complex dimensional spectroscopic data set characterized by its lack of reproducibility. The data under analysis are taken from an X-ray spectroscopic analysis of a rose window in a famous ancient Gothic Spanish cathedral. The main aim of this study is to classify each sample by its date and place of origin, so as to facilitate the restoration of these and other historical stained glass windows. Thus, having ascertained the sample’s chemical composition and degree of conservation, this technique contributes to identifying different areas and periods in which the stained glass panels were produced. The combined method proposed in this study is compared with a classical statistical model that uses principal component analysis (PCA) as a pre-processing step, and with some other unsupervised models such as maximum likelihood Hebbian learning (MLHL) and the application of the SOM without a pre-processing step. In the final case, a comparison of the convergence processes was performed to examine the efficacy of the CMLHL/SOM combined model.

A new cleaning method for historic stained glass windows

Abstract Historical stained glass has a clear tendency to form a crusted layer on its surface due to the environmental exposure. One of the most delicate aspects to be faced during the restoration of historic glass windows is the cleaning of these thick corrosion crusts. For several centuries, stained glass windows have been cleaned using damaging mechanical (scalpel) and chemical (high acidic or alkaline solutions) methods. Today's understanding of the cleaning process comprises two complementary aims: improving the readability of the glass and reducing the weathering process of the historical glass. The act of removing deposits and encrustations resulting from corrosion should not endanger the artwork itself. Mechanical methods, cleaning solutions or gel pads are now being developed. However, these methods could present further problems. In this study, we examine a new cleaning method that can be employed to remove encrustations in a quick and efficient way. Results up to now, obtained on specific stained glass windows are promising; further researches are in process for other cases. We propose an optimized solution to dissolve calcium carbonates and lead sulphates from Avila Cathedral glass windows crust. This system is tailored to control pH, temperature, conductivity and concentration of Ca2+. Continuous on-line analysis of these parameters allows us to monitor the cleaning process. In particular, the Ca2+ concentration in the cleaning solution is controlled by means of a Ca2+ ion selective analyzer.

Patination of historical stained windows lead cames from different European locations

Lead patination is a well-known phenomenon that occurs when lead is exposed to the atmosphere. A thin film mainly composed of insoluble lead salts is then formed on its surface, protecting lead against further corrosion. A study of the superficial patination of an ensemble of historical stained glass windows lead cames from different European locations (Belgium, Germany, Holland, Spain and Poland) and different chronologies (from 13th to 20th centuries) is reported in this paper. The main goals of the research were to characterise, both morphological and chemically, the patinas formed on their surfaces and to assess the weathering factors influencing the development of these patinas. Conventional optical microscopy (OM), scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis (EDX) and micro-Raman spectroscopy were used to determine the composition of the patinas. The resulting data have proved to be very useful in establishing the degree of advance of the patination process, which seems to be directly influenced by the environmental conditions to which the lead cames were exposed rather than by chronology of the samples. The results have also provided outstanding data to make decisions in conservation/restoration issues of such historical materials.

The shielding effect of the protective glazing of historical stained glass windows from an atmospheric chemistry perspective: Case study Sainte Chapelle, Paris

Atmospheric pollutants, gases as well as particulate, have been pointed out as a major cause of weathering of historic stained glass windows. Although conservators did not succeed in stopping or reversing the ensuing damage up to date, a slower rate of destruction to maintain the grandeur of the artifact is certainly achievable, by installing a protective glazing (PG). Measurements were carried out for a period of 1 year in the Sainte Chapelle in Paris, France, in order to integrate the influence of some major pollutants and acidifying substances indoors, and outdoors, as well as in the interspace, created by the PG. The concentrations of SO 2, NO 2 and O 3 were assessed using passive diffusion tubes. The PG reduced SO 2 and O 3 pollutant exposure of the stained glass windows by 80% relative to the outdoor concentrations. NO 2 concentrations remained almost the same inside, outside and in the interspace; however, previous studies showed that even in high concentrations of NO 2 accompanied by low concentrations of SO 2 the degradation of this kind of glass is modest. The results of bulk particle analyses by energy-dispersive X-ray fluorescence indicated the accumulation and re-suspension of particles as the main factor of elevated concentration of elements inside of Sainte Chapelle. The abundance and type of particles obtained by electron probe X-ray micro analysis were slightly different in the three measured areas. The main distinction is the occurrence of CaSO 4 particles inside and in the interspace. In conclusion, the installation of a PG in Sainte Chapelle seems to be appropriate.

Study of glasses with grisailles from historic stained glass windows of the cathedral of León (Spain)

This work concerns the study of grisailles of historic glass samples from stained glass windows of the Cathedral of León, which were removed during the restoration carried out in 19th century. Both the glass samples and their coloured grisailles showed very different chemical composition and macroscopic heterogeneity. As a general rule their deterioration degree is rather moderate, maybe due to the pieces removal that preserve them from the high atmospheric pollution occurred in the last century. The present research pointed out the physical characteristics, chemical compositions and deterioration degree of the samples selected from the most important Spanish ensemble of Medieval and Renaissance stained glass windows. Moreover, this work offers sufficient results to be compared with those formerly obtained for other stained glass windows from European cathedrals and churches.

Corrosion behaviour of R 2O–CaO–SiO 2 glasses submitted to accelerated weathering

Four glasses in the R 2O–CaO–SiO 2 (R = Na, K) system, following similar compositions to historical glasses used for production of stained glass windows, were prepared with different CaO/R 2O ratio. The samples were submitted to accelerated weathering test under different temperature and relative humidity conditions, as well as under controlled SO 2-polluted atmosphere. The experimental set up was selected to simulate the main conditions responsible for the deep deterioration submitted by the historical stained glass windows. Such damage has been very important during the last century, as a consequence of highly polluted industrial environments. As far as the results concern, it has been shown that 400 cycles of variable temperature and humidity are capable to develop pits on the glass surface, its shape and intensity depending on the glass composition. When weathering cycles were carried out with 10 ppm SO 2 under high humidity conditions, calcium carbonate crystals appeared upon the glass surface, whereas calcium sulphate crystallisation occurred for higher SO 2 concentration. The mechanism of chemical damage has been proposed and discussed in terms of the reaction between the Ca 2+-ions leached from the glass sample and the environmental SO 2. The former whole reaction occurred through an intermediate stage: the calcium carbonate crystallisation. That salt was displaced by sulphate only when the SO 2 concentration was high enough.

Weathering effects on materials from historical stained glass windows

A selection of materials (stained glasses, lead cames, support elements and putty) from historical stained glass windows of different periods (13th-19th centuries) have been studied. Optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction were used as characterization techniques. Degradation of historical stained glass windows is due to the particular chemical composition oftlie materials used for their production: stained glasses, lead network, metallic support elements and refilling putty. However, the presence of a given chemical composition is not the only factor involved in the degradation process. It is necessary the occurrence of other external factors that contribute to the development and progress of alteration problems in the materials mentioned above. The presence of gaseous pollution in the air produces a negative interaction with the surface of the stained glass windows materials. Firstly, the stained glasses and the grisailles begin a dealkalinisation process and a silica gel layer is formed during the early contact between the glasses and the wet environment. After that, insoluble salt deposits and corrosion crusts are formed as a consequence of a deeper chemical attack which results in a depolymerisation of the glass network. The lead cames and the metallic support elements are also altered by weathering. Such materials are oxidized and both pits and crusts appear on their surfaces. The transport of ions and other substances from the corrosion crusts of the metallic elements gives rise new deposits upon the stained glasses, which could intensify their own degradation processes. The putty experiments a noticeable shrinkage and cracking. Likewise, adverse environmental conditions favour the transport of putty substances towards the other materials of the stained glass window, thereby increasing the crusts thickness and adding elements that contribute to the total alteration of the stained glass window.

Weathering of glass in moist and polluted air

During the present century, stained glass windows in European cathedrals have shown a rapid deterioration due to weathering. It is widely believed that this rapid deterioration is a result of airborne pollutants not present for most of the 6–8 centuries since these cathedrals were built. To explore this idea, we have exposed soda-lime glass samples to ambients in which temperature, relative humidity (RH), and pollutant (SO 2 and NO 2) concentration were systematically varied. After exposure, the surfaces of these glass samples were analyzed using nuclear reaction analysis (NRA) (to measure hydrogen profiles) and Rutherford backscattering. Glasses subject to cracking during hydration, such as the glass used in many historic stained glass windows, are also discussed.

Alteration processes of medieval stained glass windows. Study and protection treatments

The anxiety caused by the fast growing decay of historical stained glass windows as a consequence of increasing environmental pollution, encouraged institutions of several countries to sponsor a series of scientific works aimed both to slow down this fast forwarding deterioration and to develop repair and preservation methods. After an initial review of the chemical composition of the stained glass windows and of the differences depending on historical epochs and origins, a discussion about chemical attack mechanisms, degradation processes and formation of superficial crusts opens up. Finally, the methodology used in their cleaning and restoration is briefly exposed and some criteria on the still polemic quest.