‘Copper and Bronze in Art’ and the Search for Rare Corrosion Products

Abstract

The information taken from David A. Scott’s book “Copper and Bronze in Art” was crucial for this research on copper corrosion products in Stuttgart. The examples discussed are: (1) the nature and variability of ‘Black Spots’ (or ‘Brown Fuzzies’), mainly copper sulfides, resulting from the action of sulfurous gases on copper containing materials at different relative humidities; (2) cupric hydroxide occurring during maritime corrosion or by cleaning, patination, and pigment synthesis (Bremen blue) when alkaline solutions are used; (3) the wondrous phenomenon of curly malachite, which does not imply any human involvement; (4) chalconatronite formed by the contact of metal to alkaline surface films on soda glass, providing sodium and carbonate ions; (5) the formation of copper formates in contact with glass by the action of electrolytes from the glass hydrolysis and the pollutant formaldehyde reacting to the formate; (6) syntheses and crystal structure determination by powder X-ray diffraction (no single crystals needed) of various basic copper acetates (‘verdigris’) with the aim to better differentiate between historic production methods.