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Adherent films of the gold-colored metal sulfides pyrite (FeS2), pyrrhotite (Fe, -$), and chalcopyrite (CuFeS2) are known to exist on metallic and nonmetallic artifacts of Classic times. Consideration of the action of bacterial consortia containing sulfate reducing bacteria (SRB) during microbiologically influenced corrosion (MIC) and analyses of appropriate trajectories on Eh-pH stability diagrams indicate that these films can be understood either as a result of natural processes over archaeological times or of deliberate pseudogilding. Methods of discriminating natural sulfide deposition from pseudogilding are suggested. 9

The data base for compounds produced during long-term corrosion of iron and copper objects is reviewed. Compounds are identified that occur in long-term but not in short-term corrosion. Where possible, the formation of these compounds is explained or at least rationalized. An effort is made to discriminate those compounds whose formation depends on microbiological action from those forming abiotically.