Characterisation of baroque tin amalgam mirrors of the historical Green Vault in Dresden |
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Authors: | O Zywitzki W Nedon T Kopte T Modes |
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Institution: | (1) Fraunhofer Institut für Elektronenstrahl- und Plasmatechnik (FEP), Winterbergstrasse 28, 01277 Dresden, Germany |
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Abstract: | The historical Green Vault, one of Europe’s most sumptuous treasure chambers, has reopened in September 2006 in the Dresden
Royal Palace. For the baroque presentation of the artworks the special properties of tin amalgam mirrors are of great importance.
A comprehensive analytic characterisation was necessary for restoration and reconstruction. The different original casting
glasses were analysed in respect of chemical composition, roughness, waviness and optical properties like chromaticity coordinates
and transmittance. The microstructure of the tin amalgam layers were investigated on metallographic cross-sections and by
X-ray diffraction. The investigations reveal that the tin amalgam layers are composed of γ-HgSn6-10 phase with a grain size between 5 and 50 μm surrounded by a thin mercury phase with about 2 wt. % tin. However the most important
property of the baroque tin amalgam mirrors is a relative low reflectivity of about 59% which is drastically lower than for
silver mirrors with a reflectivity of about 96%. According to the characterisation results a suitable glass for reconstruction
was selected. The mirror layers were produced by historical tin amalgam technology for the rooms not destroyed by bombarding
of Dresden in February 1945. For the completely destroyed Jewel Room pure tin layers were deposited by magnetron sputtering.
The results show that this new technology enables an adequate substitute for the original tin amalgam layers.
PACS 61.66.-f; 74.25.Gz; 61.10.Nz; 68.37.Hk |
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