Scientific Investigation of Glass Mosaic. Tesserae from the 8th Century AD. Archeological Site of Qusayr’ Amra (Jordan)

Glass mosaic tesserae can be divided into two main groups, i.e., coloured glass tesserae and metal leaf tesserae.Coloured tesserae are made of coloured transparent glass in which opacifying particles (crystals or bubbles) are dispersed in order to reduce their transparency and colour intensity. White tesserae are obtained from colourless glass by adding opacifier crystals, while increasing additions o these crystals to coloured glass allow progressively ligher tones to be obtained. Tesserae can be also coloured with pigment particles (yellow, red and orange) dispersed in a coloured or colourless glass.

Metal leaf tesserae are composite materials made of a thin gold or silver leaf hot sand-whiched between two glass layers. These tesserae were obtained by cutting cakes consisting of a layer of poured glass (the support, less than 10 mm thick), a thin beaten gold leaf. the cartellina, protecting the gold leaf and increasing its brilliance. […]

The aim of this study was to determine the chemical composition of the glass tesserae from Qusayr’ Amra and identify colourants and opacifiers. These data were then compared with the database of analyses of glass tesserae from other mosaics of the same period in order to ascertain similarities and differences. It is known that the mosaics used in this early Islamic building are close in their form, colours and techniques to the late Christian buildings. […]

Contents of the article:
Introduction
Glass mosaic tesserae
Glass production
Aim of ghe analytical investigations
Sampling and analytical methods
Results
– Base glass
– Coloured tesserae
– Opacifiers
– Metal leaf tesserae
Conclusions
Notes

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By Marco Verità, Paola Santopadre, Giovanna De Palma

Apparso su Bollettino ICR 32 (Gennaio-Giugno 2016; stampato in aprile 2017) – pagine 5-20 + abstract in inglese

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