Definitions for "Firescale"
Keywords:  cupric, sterling, purple, stain, copper
A black layer of cupric oxide (CuO) that forms on the surface of metal containing copper, such as silver, when the metal is heated, such as occurs in soldering.
A purple stain that develops in sterling when oxygen penetrates the outer surface of an object during brazing, oxidizing the copper content. Fine silver is left on the surface when sulfuric acid chemically removes the oxidized copper, though copper may be oxidized below the surface. Colonial pieces will show this purple stain after many years of polishing.
An oxide of copper that forms within sterling and gold alloys when heated, particularly in the presence of free oxygen. It appears as a purple to black stain.
Keywords:  flaking
Firing Flaking