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Eingeladener Vortrag
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Diese Untersuchungen erfordern die Zusammenarbeit von Naturwissenschaftlern, Denkmalpflegern und Werkstätten. In einem vierjährigen Verbundprojekt wurden alle praxisrelevanten Probleme bearbeitet. Die BAM durchgeführten Untersuchungen betrafen sowohl die Materialcharakterisierung, Schadensanalyse und Ursachenforschung als auch die Entwicklung von Methoden zur Konservierung und Restaurierung.
Dürfen Glasmalereien des 19. Jahrhunderts bei der Restaurierung einem Neubrand unterzogen werden?
(2001)
Cleaning - A balancing act
(2006)
This text originally appeared as chapter 5, 'Reinigung - Eine Gratwanderung' (pp. 101-28) in A. Wolff (ed.), Restaurierung und Konservierung historischer Glasmalereien, Mainz, 2000.
Within the context of this research programme, scientists and conservators collaborated to assess various cleaning methods for historical stained glass. For cleaning glass surfaces there are the mechanical methods already being applied in most workshops, as well as the new chemical cleaning possibilities. Laboratory experiments were conducted initially on model glass in order to test the effectiveness and damage potential of these various methods; the model glass was examined both before and after cleaning by means of light microscopy and infra-red spectroscopy. In addition to this, cleaning tests were carried out on samples of original glass; electron-ray micro-analysis was also used to evaluate the results of these tests. The model-glass samples were corroded in advance by accelerated weathering in an attempt to simulate the damage seen on medieval glass. Enough model glass was prepared to allow any number of series of experiments to be carried out, in order to compare the effectiveness and suitability of the various chemical and mechanical methods and techniques.
For the mechanical cleaning tests, a wide range of selected tools was tested by different conservators on pre-corroded model glass. This showed clearly that the success (or lack of it) of a cleaning episode was determined not just the choice of tool, but by the skill with which conservator wielded it. This observation was later confirmed by research on samples of original glass. Insensitive handling of tools or unsuitable tools could damage or completely destroy the gel layer. The gel layer should not be damaged, as this leads to increased levels of corrosion subsequently, though the encrustations should be reduced, as their hygroscopic qualities accelerate the corrosion processes.
At the next stage, chemical cleaning methods were tested, and the results of cleaning with organic solvents (toluene, ethanol, acetone, etc.) and water-based solutions (oxalic acids, EDTA, ammoniac, etc.) compared with one another and evaluated. It became clear that strongly acidic and alkaline solutions, depending on the condition of the surface, could cause damage or have uncontrollable consequences.
In the specific case of the glass from Erfurt Cathedral, for whose firmly fixed, very hard, opaque encrustations mechanical methods proved to be either ineffective or damaging to the glass, new chemical cleaning possibilities had to be found. Following comprehensive preliminary tests on model glass, various types of ion-exchanger and ammonium-carbonate solution were chosen. Both methods were successful in improving the transparency of some (but not all) of the samples.
The experiments with the original material from Erfurt Cathedral clearly showed that successful cleaning was dependent on the particular composition of the encrustation. Really gentle cleaning can be achieved by chemical means, though only when the chemical agents are tailored to individual damage situations; this can only be achieved when scientific analysis is undertaken in tandem with the cleaning processes.
The assessment of these mechanical and chemical cleaning methods was oriented towards treating corrosion on sensitive medieval glass. Nineteenth-century glass is generally less sensitive, though cleaning of this material must also be careful and very gentle. Scientific analysis alone is not enough to determine the choice of cleaning method, but can act as an aid to the conservator in selecting the right cleaning agent and method.
Aus der Abstellkammer ins Labor - Wissenschaftler unterstützen die Restaurierung von Glasfenstern
(2008)
The effect of climate and dust on the state of preservation of historic stained glass windows
(2010)
The emission of volatile organic compounds (VOC) of materials for wrapping, transportation and storage of stained glass windows were investigated by direct thermal desorption. The analysis was performed with thermal desorption in combination with gas chromatography and mass spectrometry. Emissions of organic acids were determined. The damage risk of volatile organic compounds, e.g. organic acids as acetic acid, propanoic acid, hexanoic acid and octanoic acid was investigated on model glasses in climate chambers. After exposure the surface of the most sensitive samples was damaged.
Based on emission measurements in exhibit cases of the former museum "Grünes Gewölbe in the Albertinum" in Dresden, Germany, the atmospheric conditions inside the show cases were determined. It can be shown that the atmospheric conditions inside the cases endanger the glass and enamel objects of art especially in show cases with low air exchange rates. Materials with high emission rates of organic acids should not be in direct contact with medieval glass for a long time and should not be used in exhibit cases. Acid emissions, especially acetic acid plays an important role during investigation of different materials for show cases and can be determined by direct thermal desorption.