Seamless gold and silver hollow bead

If you heat gold to about 650°F (343°C), its molecules not only become excited, they actually show changes in their electron rings. In an article published on the Orchid Forum (www.ganoksin.com), Charles Lewton-Brain suggests that this change might explain the fascinating ease with which gold bonds to other metals at that temperature. This phenomenon is exploited beautifully in keum-boo (also spelled kum-boo and kum-bu), a technique for fusing pure gold to silver using only low heat and pressure (no solder) in order to make a surface decoration. This process originated long ago in Korea, where the symbol “keum” means “gold” and “boo” means “attached.”

With keum-boo’s rising popularity, it’s easy to find ultra-thin 24k or 22k gold foil. However, I prefer to make my own. The thin, commercially available foil stuck to my silver almost instantly. My slightly thicker handmade version, however, doesn’t stick immediately. So, I have enough time to adjust the placement of the gold and position it exactly where I want it in the design.

Find out how to make your own keum-boo gold sheet, and see tips on working with gold and silver below. For step-by-step project instructions, click here to download the free project PDF.

Materials

• Fine-silver sheet: 22-gauge (0.6 mm), 1 x 2 in. (25.5 x 51 mm)
• Gold (choose from):
  - 24k gold: scrap or casting grain for melting, 2–4 g
  - 22k–24k gold foil
• Plumber’s epoxy putty

Tools & supplies

• Circle template (optional)
• Torch station: torch, charcoal block, pickle pot with pickle, flux, copper tongs, binding wire (optional), pick (optional)
• Brass brush: soft
• Jeweler’s saw with 4/0 blades; or disk cutter
• Dapping block, punches (hemispherical dapping block preferred)
• Utility hammer or rawhide mallet
• Sandpaper: various grits, including 320 grit
• Permanent marker
• Scribe or awl
• Steel bench block
• Center punch
• Bench pin
• Flex shaft, 1.0 mm drill bit
• Needle files
• Locking tweezers: old or inexpensive
• Utility pliers
• Sanding disks: fine (optional)
• Supplies for rolling your own gold sheet (optional):
  - Rolling mill
  - Calipers or metal gauge
  - scrap sheets copper or brass
• Decorative paper-cutting punches or metal shears
• Pyrex glass or steel burnisher
• Craft knife or tweezers
• Jeweler’s files: round, various cuts
• Hair dryer or heat gun
• Scrap wire
• Finishing items (choose from):
  - Liver of sulfur, baking soda
• Renaissance Wax or Krylon Matte Spray Lacquer

Make your own keum-boo gold sheet 

Select a new charcoal block, or sand an old one to remove contaminants from the surface. Use a soldering pick to carve a small depression in the block.

Place 24k gold casting grain or scraps into the depression. (You won’t need much; I used less than 2 g of gold for my bead.) Heat the gold with a large flame until the gold melts [A]. Let it cool until the red color disappears (working in a darkened room is best), and then quench it. There’s no need to pickle it because it’s pure gold.

Insert the small gold ball between the rollers of your rolling mill. Adjust the rollers until they are tight against the ball, and roll it. To create a strip, roll the gold four to six times in one direction, tightening the rollers with each pass, until the gold is work-hardened. To anneal the gold strip, heat your charcoal block with your torch until it turns a dull black-red. Remove the torch and place the strip on the hot block. Allow it to cool, and then quench it.

When the rollers are almost completely tight [B], remove the gold strip, sandwich it between two brass or copper sheets, and roll it again to make it even thinner. Check the gauge of the gold strip with calipers or a metal gauge. Gold must be thinner than 32 gauge (0.20 mm) to adhere properly. I prefer mine around 36 gauge (0.13 mm). When the gold strip is the desired gauge, don’t anneal it; leave it work-hardened so you can cut the shapes without distorting them.

Process photos by Marilyn O’Hara.

Want the goods on gold? 

Is your gold too thick?

Gold that is too thick is the main reason keum-boo doesn’t adhere. If you have rolled yours on the last setting of your mill, sandwich your gold between brass or copper plates and roll it again. 

Is your gold and/or silver clean?

Charcoal residue can prevent the gold from adhering, so be sure to clean your metal before trying to fuse it.

Do you have bubbles?

If so, use a pin or the tip of a craft knife to poke a hole into the gold over the bubble. Burnish toward the hole, pushing the air out as you heat and adhere the gold. Once the gold is fused, it’s unlikely that you’ll see the tiny hole.

Is your gold too stiff and won’t stay where you put it?

When you’re working on curved surfaces, it’s helpful to anneal the gold first. It’s easy to melt the thin gold sheet if you use your torch directly on the metal. Instead, heat a charcoal block, and then place the gold onto the heated spot until it’s annealed. Quench the gold when the dull red color disappears from the charcoal.

Does your gold still refuse to stick?

If it becomes too frustrating to adhere the gold, you can use a little saliva on the back of your gold to hold it on the silver bead where you want it. Let it dry and then heat up the charcoal block and bead, being careful not to overheat the gold. Then burnish the gold. The saliva acts as an organic binder to hold the gold in position long enough for you to burnish it in place.

What about sterling silver?

Due to its molecular properties, fine silver works best for keum-boo. So, if you want to use sterling silver, you have to build up a thin layer of fine silver on its surface for the gold to adhere to. This process is called “depletion guilding.”

Use a torch with a soft, bushy flame to heat the sterling silver, then pickle it and gently brush it with a brass brush. Repeat until your sterling no longer turns black when it’s heated. This indicates that there is enough fine silver built up on the surface for the gold to stick to. To protect the fine silver, don’t use the brass brush on the final heating.