Keum-boo
Keum-boo is a Korean metalworking technique that bonds thin gold foil to silver using heat and pressure. It can create defined golden areas and patterns against a silver surface. The name describes surface work, not a particular shape of jewellery.
Gold on silver is not solid gold
An object decorated with keum-boo can have a silver body even when parts of its surface are covered in gold. The foil described in the traditional technique is fine gold. This does not mean that the entire object has the same fineness as the foil. Keep information about the underlying metal, surface treatment and any fineness marks separate in the description.
Documentation and condition
Two-colour metal alone does not establish keum-boo. Request the maker's technical notes or other documentation before selling an object under that description. Examine wear in the golden areas and photograph the transitions between gold and silver. Do not try to polish away irregularities before the surface construction is understood. A signed piece still needs examination as an individual object, and the technique alone does not justify attribution to a particular artist.
Sources
V&A: A guide to metalworking techniques; The Goldsmiths' Centre: Keum-Boo.
