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Problems with Oxidation and Corrosion Merovingian Scramasax, about AD 500-700 Iron, copper alloy (brass), gold foil, gold wire, gemstones 21-3/8 x 2-1/2 inches Purchase from the J. H. Wade Fund 1926.429 Metals or alloys that are resistant to oxidation or corrosion are called "noble." This single-edged knife, on view in Gallery 211, was manufactured using three different metals: gold, copper, and iron. Since gold is the most noble metal, the gold elements of the knife remain uncorroded, while the "baser" metals such as copper and iron have corroded. However, the copper in the copper-alloy fittings is more noble than the baser iron. Thus the corrosion of the copper-alloy is limited to the formation of a green corrosion layer (called a patina) on the surface while the structural features remain well preserved. In contrast, the iron blade has been almost completely mineralized, or converted back to an iron ore.