Scientific study of ancient jewelry has usually been undertaken in order to establish criteria for determining provenance and age of objects. Gold has posed particular problems because it has been used for trade and is frequently mixed, alloyed, refined, and reused. Gold-silver-copper ratios of Roman and post-Roman goldwork support other evidence for dating, but trace element identification is impossible. Platinoid inclusions have demonstrated that more gold originated from placers than in vein deposits, as had originally been thought. Verification of forgery is easier to ascertain than proof of authentication. Changes in gold objects due to burial conditions include diffusion of elements to the alloy surface, cathodic protection, precipitation coatings, gold solution and reprecipitation, and attack from organic agents.