gems, Egyptian blue, egyptian green, wollastonite, azurite, malachite, chrysocolla, pigments

We report the discovery of a severe and advanced deterioration process affecting Egyptian Blue, Green Frit, and Egyptian Faience in ancient Egyptian decorations and paintings. This process begins with the devitrification of copper- and chlorine-bearing glass and glaze, followed by the leaching of copper and chlorine ions into migrating solutions. These ions react with calcium carbonate in the stucco or with sodium chloride-rich solutions, leading to the precipitation of basic copper chloride (atacamite or paratacamite). These compounds deposit on the surface of the pigment layer or glaze, within its interstices, and in the underlying stucco or plaster. As a result, the original blue pigment shifts to a faint green, while the pigment layers or glaze become highly friable and spongy, ultimately disintegrating into fine powder. This degradation culminates in the denudation and final destruction of the painted surfaces, leaving bare reliefs.