Keum-boo Pillow Pendant
The art of gold foil on silver.
by Christine Dhein

In the ancient Korean technique of keum-boo, pure gold foil is bonded to the surface of another pure metal, such as fine silver. This produces a rich gold color, while using very little gold. The simplicity of this technique makes it an easy, inexpensive way to add gold to your work.

Gold is attached to silver through a diffusion bond, an intermingling of molecules where the two metals meet. When pure metals are brought to the correct temperature, 500-700° F, the molecules become excited and bond easily when pressure is added, to create a permanent bond. This diffusion bond occurs far below the soldering temperature for either metal.

Sterling silver must be depletion gilded by repeated heating and pickling before it can be used for keum-boo. This process removes the base metals from an alloy, leaving a layer of pure metal on the surface.

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	• Sterling silver sheet, 24-gauge 1-1/4" x 2-1/2" or larger • 24K gold keum-boo foil, .01-.05mm thick • 3mm rubber neck cable, 14-18" in length • 1 jump ring, made from 24-gauge wire with an ID (inside diameter) of 3-3.5mm • 1 jump ring made from 16-gauge wire with an ID of 4mm • Easy silver paste solder • Torch • Charcoal block • Pickle pot and warm pickle solution • Copper or plastic tongs • Bowl with a saturated solution of baking soda and water • Bowl of clean water • Brass brush • Liquid dish soap • Tracing paper • Sharp scissors (I prefer Joyce Chen® cooking shears) • Craft punch • Clean tweezers • Fine-tipped paintbrush • Hotplate with variable heat control • 20-gauge steel sheet, slightly smaller than hotplate burner or 14-gauge brass or nickel silver sheet • Ceramic tile • Medium-weight cotton or leather gloves (Must be a good fit to perform delicate work) • Agate or curved steel burnisher • Fine pointed needle • Disk cutter • Heavy hammer • Short length of 1/4" wooden dowel • Wooden dapping block and punch • Mallet • Center punch • Small drill bit • Flexible shaft • Large permanent marker • Dividers • Flat file • Round needle file • Firecoat (50/50 solution mixture of boric acid and denatured alcohol) • Solder pick • 2 pairs of chain nose pliers or 1 chain nose and one flat nose pliers • Sanding sticks and polishing papersOptional tools • Optivisor® • Fine point permanent marker • Ruler • Craft scissors • Steel dapping block and punches • Liver-of-sulfur • X-Acto® knife
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Christine Dhein is a San-Francisco based jewelry designer who works primarily with precious metals, rubber and diamonds. She is also the Assistant Director of the Revere Academy where she teaches keum-boo and fabrication. Her most recent work, Sexi Reware, a collection of recycled rubber and plastic fashion accessories, created in collaboration with Emiko Oye, debuted on the runway in May 2004. To contact Christine, visit www.seximetal.com or call 415-407-5389. Try your skills with more step-by-step projects here! Search for more projects available for purchase through StepbyStepJewelry.com Instant Article Reprints Looking for supplies? Check out our Online Classifieds for great deals. Or, search for suppliers by keyword in our Product & Dealer Search.

Preparing the metal.
Insert a piece of silver sheet into the slot in the disk-cutting die. Check for a minimum clearance of 5mm on each side of the hole. Place the cutting die on a soft surface, such as wood. If possible, use a surface with a recessed area to catch the cut disks.

Position the circle punch in the die with the cutting end face down against the sheet. Keep the sheet and punch in alignment and hammer the punch through the sheet with a heavy hammer. Remove the disk. Use a wooden dowel to hammer the punch all the way through the cutting die. Repeat to cut the second disk.

Place the clean sterling disks directly on the charcoal block. Heat evenly with a torch using a neutral flame until the surface turns dark grey.

Do not overheat. Quench in water. Pickle until the surface becomes bright white. Remove from the pickle with copper tongs. Neutralize in a baking soda solution. Burnish the surface with a brass brush and soapy water.

Rinse and repeat 3-6 times. For beginners, I recommend 5-6 cycles to ensure a thick layer of fine silver. The surface of depletion-gilded sterling remains white when heated. Handle the piece by the edges after the final brass brushing to keep the surface clean.

Always handle the foil carefully with tweezers and work over a clean surface. Do not touch the foil with your fingers. Draw your design on thick tracing paper, fold it into a pocket and place the foil inside. The paper supports the foil to prevent folds and tears. Cut the gold to shape with a sharp scissors or use craft punches and craft scissors to easily cut intricate shapes.

Handle the disks by the edges and use tweezers or a damp brush to place the foil onto your cut disks. If the pattern is intricate, use a fine-tipped permanent marker to draw an outline, slightly larger than your shape, on the disks. Allow the piece to dry before heating.

Burnishing.
Agate burnishers work best for thinner foil, curved steel burnishers for thicker foil. Gold will stick to steel if it gets too hot. Quench steel burnishers in water. Do not quench agate burnishers, as they will fracture. Use the belly, or the section of the tool with the broadest area of contact.

Work on a heat-resistant surface. Place a sheet of steel, nickel, or brass on top of the burner. Adjust the hotplate to 500-700°F. An oven thermometer can be used to find the exact temperature. However, the correct temperature can easily be found through experimentation with a practice piece. Steel will start to turn blue when it reaches the correct temperature for keum-boo. Mark the optimal control setting for future reference.

Use gloves while working over heat. Carefully place the dry piece from Step 4 on the hot steel plate. Hold the work securely with tweezers. Tack foil in place by pressing lightly in the center of each shape. Starting in the center of each gold shape, burnish the entire piece. Use light, even pressure and burnish in a circular motion. Work from the center toward the edges to avoid trapping air bubbles between the gold foil and the silver. Give special attention to each edge to be sure it is tacked down.

Remove the piece from the heat and allow it to air cool. Do not quench! Place the piece on ceramic tile to speed cooling.

Use an Optivisor® and X-Acto® knife to examine the edges of the foil for a secure bond. Surface should be smooth without bumps or irregularities.

Remove any small bubbles with additional burnishing on the hotplate. Pierce any large bubbles before reburnishing. To repair tears, cut a small piece of foil to cover the tear and burnish as usual. Carefully sand the surface to even out the gold thickness if necessary.

Fabricating the pillow pendant.
Traditionally, all soldering is done on a piece before the keum-boo process is performed. It is possible to solder on a piece after you’ve applied the gold, but if it’s overheated during soldering, bubbling may occur. Additionally, too much heat can cause the gold to diffuse into the surface and visually disappear. Be very careful not to overheat during soldering.

Coat the finished keum-boo disks with firecoat. Place them on a charcoal block and anneal by heating evenly with a torch, using reducing flame, until the silver appears dull red in color. Beginners can turn off overhead and bench lights to see this subtle color. The annealing temperature is higher than the temperature for depletion guilding but still far lower than the soldering temperature. Do not overheat. Allow the piece to air cool. Pickle until the surface becomes bright white. Remove them from the pickle, neutralize, rinse and dry.

Place one silver disk with the keum-boo side down into the largest depression in the wooden dapping block. Use the dapping punch to dome the disk.

Start at the edge and work in a circular pattern around the edge of the disk. On the second pass, bring the punch closer to the center and work your way around again.

Repeat until you reach the center of the circle. Repeat with the second disk. Steel dapping blocks and punches can be used to create more volume.

Make a guide with a center punch and drill a hole in one half of the dome to allow gases to escape during soldering. Remove the bur.

Sand or file the edges of each dapped circle until the seams meet perfectly when assembled.

The smaller jump ring will be used as a bail at the top of the pendant. Measure the outside diameter of this jump ring with a divider. Transfer this measurement to each half of the pendant by scribing lines with both divider legs.

Coloring the metal with a thick permanent marker before scribing makes the lines more visible. In the edge of each dapped disk, file a half round opening toward the inside of each scribed line with a round needle file. When filing is complete, the jump ring should rest between the two pillow halves, allowing the seams to meet without gaps.

Carve a recessed area into your charcoal block as a seat for the pendant. Coat the two dapped disks and jump ring with firecoat. Place the bottom half of the pendant on the charcoal block, seam up. Squeeze a generous amount of easy silver paste solder around the inside of the seam on the top piece.

Paste solder contains flux so additional flux is unnecessary. Remove excess solder from the outside of the piece before soldering.

Using solder to hold it in place, align the jump ring and the top disk with the notches on the bottom half. Heat evenly with a neutral flame to solder.

As soon as the solder flows, draw the solder pick along the seam to remove oxides. Air cool. If the joint is good, the seam will appear as a shiny silver line. Any dark areas indicate where the solder did not flow. If necessary, apply additional solder to the seam and reflow. Boil it in water to remove the flux.

Carefully sand the solder seam with 400- and 600-grit sandpaper until it blends into the piece.

If you have foil near the seam, be careful not to sand the gold.

Give the piece a satin finish with a brass brush and soapy water or polish it with a polishing cloth or papers.

The piece can be darkened with an oxidizing agent, such as liver-of-sulfur. Attach your finished piece to a rubber neck cable with the larger jump ring and enjoy wearing your new keum-boo creation.

Resources: Manufactured 4" x 4" sheets of 24K keum-boo foil, 0.01mm thick, and agate burnishers can be purchased from AllCraft.