Objects made from a gold-copper alloy including silver (tumbaga) are described: many have a two or three color surface pattern due to intentional depletion gilding. The objects were analyzed by a variety of techniques and examined visually and microscopically. Various methods of depletion gilding were reproduced in the laboratory; the results are discussed and compared with documentary evidence. It seems likely that a variety of etching techniques using plant juices was employed -- techniques unique to South America. -- AATA