Firescale
From Wikipedia, the free encyclopedia
Firescale, also known as firestain, is a red or purple stain that appears on mixtures of silver and copper, such as sterling silver. At high temperatures, oxygen mixes with the copper to form cuprous oxide and then cupric oxide. Attempts to reduce this problem usually involve replacing oxygen with another gas such as hydrogen or ammonia.
With a very high copper content, this may appear on gold mixtures.
