Keum-boo is an ancient Korea

Korea

Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

n gilding

Gilding

The term gilding covers a number of decorative techniques for applying fine gold leaf or powder to solid surfaces such as wood, stone, or metal to give a thin coating of gold. A gilded object is described as "gilt"...

 technique used to apply thin sheets of gold

Gold

Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...

 to silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

, to make silver-gilt

Silver-gilt

Silver-gilt or gilded/gilt silver, sometimes known in American English by the French term vermeil, is silver gilded with gold. Most large objects made in goldsmithing that appear to be gold are actually silver-gilt; for example most sporting trophies, medals , and many crown jewels...

. Traditionally, this technique is accomplished by first depleting the surface of sterling silver

Sterling silver

Sterling silver is an alloy of silver containing 92.5% by mass of silver and 7.5% by mass of other metals, usually copper. The sterling silver standard has a minimum millesimal fineness of 925....

 to bring up a thin layer of fine silver. Then 24 carat gold foil

Metal leaf

Metal leaf, also called composition leaf or schlagmetal, is a thin foil used for decoration. Metal leaf can come in many different shades. Some metal leaf may look like gold leaf but not contain any real gold...

 is applied with heat and pressure - mechanical gilding - to produce a permanent diffusion

Diffusion

Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...

 bond.

Pure precious metals such as gold and silver have a very similar atomic structure and therefore have a good potential for bonding. Heating these metals to a temperature between 500-700°F increases the movement of the atoms. When pressure is added, this causes an electron exchange at the surface between the two metals, creating a permanent diffusion bond. This diffusion bond occurs far below the soldering

Brazing

Brazing is a metal-joining process whereby a filler metal is heated above and distributed between two or more close-fitting parts by capillary action. The filler metal is brought slightly above its melting temperature while protected by a suitable atmosphere, usually a flux...

 temperature for either metal. (Dhein, 2004)

Examples of this technique have probably been observed, but not positively identified on pieces from the second half of the first millennium B.C. and from the early first millennium A.D. (Oddy,1981)

This technique is used in many cultures, including Chinese, Japanese and in the West to bond gold to other metals, including iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

, aluminum, gold alloys, white gold, palladium

Palladium

Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...

 and platinum

Platinum

Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is a dense, malleable, ductile, precious, gray-white transition metal...

. Foil made from gold alloys can be applied to silver and other metals by first depletion gilding

Depletion gilding

Depletion gilding is a method for producing a layer of nearly pure gold on an object made of gold alloy by removing the other metals from its surface. It is sometimes referred to as a "surface enrichment" process.-Process:...

the surface of the foil. (Lewton-Brain, 1987–1993)