text: The term depletion gilding usually refers to the production of a layer of gold. However, it can also be used to produce a layer that is an alloy of gold and silver, sometimes referred to as electrum. Certain chemicals, such as oxalic acid, attack copper but do not affect either silver or gold. Using such a chemical, it is possible to remove only the copper in an alloy, leaving both silver and the gold behind. Thus, if the original object is composed of copper, silver, and gold, it can be given a gold surface by removing both silver and copper, or an electrum surface by removing only the copper.
  Likewise, with an appropriate chemical, a layer of nearly pure silver can be produced on an object made of copper and silver. For instance, sterling silver can be depleted—depletion silvering—to produce a fine silver surface, perhaps as preamble to application of gold, as in the Keum-boo technique.
  However, in the majority of cases depletion gilding is in fact used to produce a gold finish, rather than one of electrum or silver.