Green-copper containing waxy paint on two Egyptian polychrome artifacts: A technical study

A green waxy paint was found on some fragments of jars at the Metropolitan Museum of Art made of Egyptian alabaster and dated to the Nineteenth Dynasty (1292-1182 BC). Four different types of particles were seen in these paints: green, blue, red-brown, and semi-transparent. The blue particles were identified as Egyptian blue. The green particles present problems as it is still not certain whether they are an original green or an altered blue particle. X-ray fluorescence revealed that copper is the main element in the green waxy paint. Fourier transform infrared spectroscopy (FTIR) found that an extra peak formed at 1588 cm −1 which correlates to organo-copper salts. Gas chromatography-mass spectrometry analysis confirmed that the binding medium of the waxy paint is aged beeswax. Laboratory experiments showed that heating beeswax with malachite, chrysocolla, verdigris, and copper acetate, as well as heating beeswax in a copper crucible, generate the diagnostic 1587-1588 cm −1 peak in the FTIR spectrum, which is also found in ancient samples. Chrysocolla, malachite, and altered Egyptian blue/green are the possible candidates for the green particle.