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With the implementation of glass casting in France in the second half of the 17th century, larger mirrors could be produced. So-called tin-mercury mirrors were made by coating glass with tin amalgam. Today, many historical mirrors are partly damaged, the image quality is compromised, and the material integrity of the mirror is threatened. The transformation from tin into an oxide starts at the surface of the amalgam and proceeds down to the glass surface. The mercury dissolves as a liquid or gaseous phase. The amalgam layer is destroyed, so that conservation is necessary. Conservators must follow strict safety precautions while handling amalgam mirrors because of possible mercury emissions and corrosion of the amalgam, during which elemental mercury accumulates near the mirror frame in droplets and is emitted into the air.
In a research project, the quantity of the mercury emissions from historical mirrors was examined and a technique to decrease these emissions was developed.
Untersuchung historischer Goldmosaike Herstellungstechnologie und charakteristische Schadensbilder
(2009)
Mit der Erfindung des Glas-Guß-Walzverfahrens eröffnete sich die Möglichkeit, größere Spiegelflächen als zuvor herzustellen. Diese sogenannten Quecksilberspiegel sind mit Zinnamalgam beschichtet. Wenn Restauratoren mit Zinnamalgamspiegeln arbeiten, müssen sie strenge Sicherheitsvorkehrungen einhalten. Häufig finden sich im Spiegelrahmen Quecksilberkugeln, die beim Öffnen herausfallen und damit gesundheitsschädliches Quecksilber freisetzen können. In einem Forschungsprojekt wurden die Quecksilberemissionen aus Zinnamalgamspiegeln gemessen und Möglichkeiten entwickelt, diese zu verringern.
Today glass is broadly used in modern architecture. For indoor applications it is possible to produce decorated glass by using enamel colours and glass painting techniques without any problems. However, this is more limited for applications out of doors. Humidity and environmental pollution attack the surface of the coating and can damage it. There are only a few colours on the market which are resistant towards acids and bases until now. Additionally, most of those colours are opaque. To extend the colour palette, chemically resistant low melting coloured glasses are being developed which are transparent and intensively toned even in thin coating thicknesses. To achieve such an ambitious aim, many parameters have to combine and act in a complex manner. New compositions of lead borosilicate, zinc borosilicate and lead-zinc borosilicate glasses were produced and milled as powder. The thermal properties as well as the environmental stability were analysed. The influence of PbO and ZnO on the thermal properties and the environmental stability were investigated. Evaluation of the fusing results shows that the production and mixture of transparent vitreous enamels for the exterior side of glasses is possible. The tests made it clear that the original materials for making the vitreous enamels must be excellently ground and prepared to achieve a satisfactory result. The method to produce durable vitreous enamels for exterior application also seems to allow the production of glass colours.