Effect of pollution on polychromed ceramic statues

Pigments of different colours used to polychrome ceramic statues have been characterized using different experimental techniques. The pigments detected in the painting layers belong to the group of natural minerals widely used in antique paintings. The polluted air and the composition of dust and crust on the ceramic surface have been analysed. Environmental pollution has altered the surface of the ceramic sculptures, destroying the polychrome, so that only small parts covered by crust or dust remain. The environment is responsible for transformation of the chemical components of the pigments. The lead compounds minium and hydrocerussite are altered to anglesite, cerussite, hydrocerussite and lead sulphide. Azurite, forming some blue colour, is hydrated to malachite which is green.Atacamite is formed by the transformation of azurite in the presence of the chloride ion from environmental pollution. The environment supplies a variety of organic compounds—mainly alkanes (produced by petrol combustion)—which are responsible for the black coating on the polychrome., which serves as nutrition for microbiological growth.