Keum Boo

Last meeting Ken Rose gave us a great demo on keum boo where he created a piece entitled “Up Sutters Creek without a gold pan.” He has graciously written a short article about the process so we can all try it in our studios! I’ll let Ken take it from here:

Kuem-boo is an old Korean technique for fusing high carat gold foil to silver and other metals, using relatively low temperatures and pressure.

The kuem-boo process, as in all jewelry processes requires planning ahead. Applying the gold foil is one of the last steps. All soldering must be done before the application of the gold foil. Riveting as well as other cold connections along with stone setting is done after completion of the kuem-boo process.

For Sutter’s Creek, I began by cutting out three pieces of sterling silver sheet. I drilled two holes for the rivets in the largest piece of silver. The holes were drilled where the top pieces of silver would cover the rivets. I positioned the silver on the slate where I wanted it and drilled the holes in the slate and the backing sheet/bail. The rivet wires were soldered into place and the two smaller pieces were sweat soldered into place. Final shaping and filing were then completed.

The piece was heated and pickled then rinsed; this process was repeated until a skin of fine silver covered the entire piece. Gold foil is very delicate and can be tricky to work with. I find the easiest way to cut the foil is to put it between the layers of a folded sheet of paper on which the design has been drawn. The silver piece is placed on a soldering screen that is on a soldering tri-pod. The piece is carefully heated from below with a torch to a temperature of 500 – 700 degrees. The gold foil is picked up with either a small brush or a burnisher to which saliva or a thin paste of gum tragacanth has been applied. If the correct temperature has been reached the foil will adhere when burnished with the burnisher.

To complete the pendant I riveted the kuem-boo piece to the black slate and the backing sheet/bail. I chose a brushed finish for the silver parts, as a highly polished silver surface would optically blend with the gold.

Chasing and Repousse: Tools

At our last meeting McKenzie Roth gave us a demo on chasing and repousse including tips on tools and technique. Here are a few pictures tips and resources to help you get started with the technique.

The first thing you need is chasing setup. This includes a chasing bowl with pitch, and a chasing hammer, and of course chasing tools. There are commercial options for for all of them, but shop made tools just work better sometimes…and they are way cooler. The chasing bowl can be made by going to your local fence supplier and getting a 6″ fence post cap, if you are planning on working larger scale 8″ caps are also available. For a rubber ring to rest the bowl on, a replacement lawnmower tire with the center knocked out works nicely. Once you have your supplies fill the fence cap with concrete, leaving about 2″ of space at the top. Fill the remainder with pitch.

Chasing bowl, hammer, and tools (and artist)

Pitch, while it can be shop made using pine resin, plaster of paris, and linseed oil, is a material that is best purchased from a commercial source. Northwest Pitchworks in Seattle, WA makes pitch in 3 grades, hard, medium and soft, and sells it for $11 per pound shipped (medium is best for general use), but McKenzie recommends red German pitch as the best. Otto Frei sells a 2 kilo (4.4lb) block for $45 (although they are calling it brown pitch) and it is available from many other sources. Either pitch will work and they are both vastly superior to the black tar pitch that was used in the past.

A chasing hammer is something that is fairly personal some people prefer a lighter hammer some heavier, some like a flat face and others prefer domed. The only advice I can give is to get one that feels good in your hand and try it out. Tools are the really fun part. The best chasing tool is a tool you have made to do a specific job so a commercial set just won’t suffice, and making chasing tools is actually pretty easy.

Start with steel. You can get commercial tool steel, but allen wrenches, garage door spring steel work equally well. If you are using repurposed steel you will have to start by annealing it. Heat until it is glowing and then let it cool slowly it should get soft enough to work. Shape your tool by filing, forging, or grinding until it reaches the shape you need. McKenzie recommended twisting the stock along the length of the tool to give her hand a more comfortable grip. When the tool is polished and ready the next step is to harden it. To do this you heat the tool until it is glowing red with no shadows and quench it in oil. When it is cool run a file over it, if the file feels like it is sliding over glass and will not cut the steel you have hardened it successfully, if not try again. The steel in this hardened state is too brittle and will shatter if you try to use it so the next step is to anneal the tool. To do this heat with a torch from the middle of the tool until color bands start to appear. When The tip of the tool is straw yellow with bands of blue and purple behind it quench it immediately.

McKenzie explaing in the finer points of Chasing and Repousse

You should now have a tool that is tempered and ready for use with. If you are just getting started make a set of about a dozen tools, copying commercial shapes. This will give you enough tools to get a sense of what shapes you like and what shapes you need and remember: you can never have enough chasing tools!

You should now have all the information you need to get your chasing setup ready! Next time I will write about chasing technique. If i missed anything or just made a typo, as always just leave a comment.

Until next time!