Keum boo is a traditional Korean technique for bonding thin gold foil onto silver. The name translates roughly as "attached gold". It has become a favourite among silver clay makers for a simple reason: keum boo works best on fine silver, and silver clay becomes 99.9% fine silver the moment it is fired. If you have already made a piece from silver clay, you have the perfect base for it.
Why keum boo and silver clay go together
Traditional silversmiths working in sterling silver have to prepare the surface before gold will bond to it. Sterling contains copper, and the copper interferes with the bond, so the metal is heated and pickled repeatedly to bring a layer of pure silver to the surface. That step is called depletion gilding, and it is fiddly.
Fired silver clay skips that entirely. Because the metal is already fine silver all the way through, the gold foil can be bonded directly to a clean, burnished surface. For a home maker with a torch and a few tools, this is the shortest path to real gold on real silver jewellery. Our complete guide to silver clay explains why the fired metal ends up so pure.
What keum boo actually does
The technique relies on diffusion. When fine silver and pure gold foil are pressed together at a moderate temperature, well below the melting point of either metal, atoms at the surface migrate across the join and the two metals bond. No solder, no glue. The gold becomes part of the surface of the silver, which is why a good keum boo piece will not peel or flake with wear.
The foil used is very thin 24 carat gold, sold specifically for keum boo. It is cut with scissors or a craft knife into whatever shapes you want: dots, leaves, stripes, or an organic patch that follows a texture in the clay.
The basic process
1. Start with a fired, clean piece. Fire your silver clay as usual, brush it, and make sure the surface is free of oil and fingerprints. A burnished or lightly polished surface bonds better than a heavily brushed, matte one.
2. Cut the foil. Handle the gold foil with tweezers or a fine brush. It is delicate and will stick to damp fingers. Cut your shapes on a clean piece of paper.
3. Heat the silver. The piece is placed on a hotplate, a steel plate over a small flame, or a kiln-top surface and brought up to a moderate, steady heat. The foil bonds within a temperature range that is well below red heat; follow the guidance that comes with your foil, since it varies slightly by supplier and thickness.
4. Place and burnish. Lay the foil on the hot silver, then rub it firmly with an agate or steel burnisher. Work from the centre outwards to push out air. The foil changes from loose to fixed as it bonds, and you will feel the difference under the burnisher. Add the next piece and repeat.
5. Cool and finish. Let the piece cool, then polish gently. Avoid aggressive abrasives over the gold; the layer is thin and can be worn through.
Design ideas for silver clay makers
Keum boo is at its best when it is used with restraint. A single gold dot on a plain silver clay ring looks far more expensive than a ring covered in it. Gold on the high points of a textured pendant catches the light while the silver recesses stay soft. A thin gold line along the edge of a pair of earrings is subtle enough for daily wear.
Because the gold sits on the surface, plan for it at the design stage. Leave a smooth area on your clay where the foil will go, and keep deep textures elsewhere.
Is it a beginner technique?
Honestly, it is a second-project technique rather than a first one. You need to be comfortable firing and finishing silver clay before adding gold. If you are new to the material, start with the silver clay starter kit, which includes the clay, a torch, tools, cubic zirconia stones and instructions, and make a couple of simple pieces. Once those are going well, keum boo is a natural next step, and the fine silver you have been making is exactly what it needs. Extra silver clay is available separately, and we ship worldwide with duties covered.
