‘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.