The occurrence and alteration of realgar on ancient Egyptian papyri

The light-fading of realgar and its polymorphs is reviewed. A variety of realgar paints were prepared using gum arabic as a binder and the line was seen to vary with the extent of grinding. Raman spectroscopy and colorimetry were used to follow the fading of realgar paint. The particles changed to pararealgar via x-realgar. The initial colour change from orange to yellow was very fast, the smallest particles being most light-sensitive. Subsequently the yellow became fainter as arsenolite was formed. Realgar was found to dissolve in. hot Meltmount and, on cooling, crystallized as beta-realgar. Realgar and its alteration products have been found oft a wide range of papyri in the British Museum. One papyrus roll had been cut into many sheets, enabling a study of realgar and orpiment paints which had been exposed to various amounts Of natural light. Both orpiment and realgar faded to arsenolite; the latter has been seen on papyri as transparent, colourless octahedral crystals. Partly faded areas contained realgar, pararealgar and x-realgar. On one sheet, haematite appeared to have been used as a replacement for realgar.