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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.
Stained glass is a particularly sensitive medium that in many churches has stillnot received sufficient protection against destructive influences of many andvarious kinds. Over long periods of time, nearly all materials are subject tochemical and physical change. The dramatic scale on which the processes of decayoften occur results from the influence of corrosive gases that are part of themix of today’s atmosphere. A basic requirement in the preservation of anyhistorical monument is therefore interdisciplinary collaboration; only the jointefforts of art historians, restorers and technicians, as well as scientists,offer a chance to protect our artistic and cultural heritage from decline.
Measures to protect, conserve and restore stained glass are carried out by glassstudios. The project on which this chapter reports provides support for thispractical work through scientific back-up. In order to clarify what are verycomplex issues, a brief explanation of the scientific/technical context followshere, to preface the exposition of the basic questions posed.