Ancient alloys, corrosion

Bronze disease is the name given to a form of corrosion of bronze and some other copper alloys, in which light blue-green outgrowths form on the surface (see Fig. 41). It is an especially obnoxious form of corrosion that particularly attacks ancient excavated bronze objects. Unless terminated by specialized treatment soon after excavation, bronze disease usually results in the complete corrosion and total destruction of the object. 

Iron and the Ferrous Alloys. Iron exposed to a moist environment reacts with water and atmospheric oxygen to form rust, a brown, crumbly corrosion product (composed of hydrated iron oxide). Initially rust forms a surface layer that is usually held in much disfavor. If an ancient iron object... 

The purified metal is hard but malleable and ductile. Its silvery white appearance can be polished to a lustrous finish, and provides about l/4th of the American 5-cent piece. Its corrosion resistance makes it good for coinage. The ancient Chinese produced an alloy called Paktong by smelting ores containing copper, nickel, and zinc thatis now known as nickel silver and is the base for high-grade silver-plated ware. 

All of these compounds are bactericidal and the ancients knew that they helped to prevent wounds from festering. Accordingly, Achilles has been represented in ancient pictures as scraping the rust or oxidation products from his bronze sword or spear into the wound of Telephusf. These oxidation products are frequently but incorrectly called verdigris, which latter is really a basic acetate of copper, and is not produced by ordinary atmospheric corrosion of the metal or its alloys. 

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