| Abstract: | SUMMARIES. The light-fading of realgar and its polymorphs is reviewed. A variety of realgar paints were prepared using gum arahic as a binder and the hue 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 p-realgar. Realgar and its alteration products have been found on 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.
CONCLUSION. Polychrome papyri have been shown often to contain arsenical pigments, and realgar has been shown to be remarkably sensitive to the effects of light. The British Museum has many papyri on which some realgar remains; such objects should have their exposure to light minimized. However, the lightfastness of partially faded realgar paint is greater than at the start of the fading period because the remaining particles of realgar are bigger. Small particle size has previously been linked to poor lightfastness [21]. Pararealgar and orpiment are of approximately the same lightfastness and, although much more stable than realgar, should still be regarded as light-sensitive. |
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