It's no secret that I love working in mixed metals - particularly oxidized silver + high karat gold. The contrast between the blackened silver and the rich yellow color of the gold has always captured my imagination. There are several ways to combine metals, but one of my favorites is Keum-Boo.
Keum-boo means "attached gold" in Korean. It's a traditional Korean gilding technique used to apply thin sheets of gold to silver. When starting with sterling silver, the first step in the process is to heat the silver to bring a thin layer of fine silver to the surface of the metal. This is called depletion gilding. After several cycles of heating and quenching the metal, it will appear a chalky white color and that's when you know the surface is ready for keum-boo.
Once the surface is prepared, I place the silver on a hot plate and heat it to around 500 degrees F. Using this heat and pressure from a special agate burnishing stick, I apply paper thin layers of 24k gold to the silver and burnish it until a permanent bond is formed.
There's a lot of science behind how this works, but the short story is this: Pure precious metals such as gold and silver are able to bond because they have a very similar atomic structure. When you heat the metal to the right temperature, the movement of the atoms increases. Add in a bit of pressure and the metals will exchange electrons at the surface, creating a permanent diffusion bond. Pretty cool, right?
The gold used in Keum-boo is as thin as a sheet of tissue paper. It can be cut into specific shapes with scissors or paper punches, but I prefer to cut or tear thin strips and apply them randomly to my piece of jewelry. Keum-boo can be very organic, or it can showcase amazingly intricate patterns.
Once I finish applying the gold, I brush the piece with a brass brush to further secure the bond and remove any loose gold. Then, I dip the piece in an oxidation solution that turns the silver black, yet leaves the gold nice and shiny for a beautiful, striking contrast.
How should you care for your Keum-boo jewelry? Although the gold bond is permanent, it is still a fairly thin layer of gold. You should be careful to remove your jewelry if you are doing anything that might result it in getting dinged or scratched - particularly in the area that has been gilded. Additionally, oxidization is not permanent. Contact with your skin, soaps, etc will cause the oxidation to patina to a gunmetal grey and then eventually back to a more shiny silver over time. Try to remove your oxidized jewelry when you take a shower, go for a swim, or other similar situations.