a copper base alloy of superior tarnish resistance consisting essentially of 7 . 0 to 8 . 5 % aluminum by weight and 1 . 5 to 2 . 5 % nickel by weight with the balance being essentially copper . the process by which the alloy is prepared is controlled so that the alloy is primarily single phased , i . e ., a face centered cubic alpha phase solid solution containing a fine dispersion of nickel aluminide compound and less than 2 volume percent of the brittle intermetallic phases known as beta and gamma . by composition control and by producing an essentially single phased microstructure , the alloys of the invention are capable of forming a stable oxide film having high tarnish resistance . the alloy , upon prolonged exposure indoors to ambient air and frequent handling , develops a very thin , tight , uniform oxide film which , although visible , is still attractive and does not mask the basic warm tone of the base metal . this film , when intact , serves to protect the underlying metal from further oxidation , and when damaged , is self - healing and reestablishes itself to provide a uniform protective and decorative film .