Alice Alper-Rein        JEWELRY BY Y2A, Ltd.
Fine Contemporary Art Jewelry in Silver and Gold
           


TIPS, TRICKS AND TECHNIQUES FOR:
ADDING GOLD TO METAL CLAY      


A.  ADDING 24K GOLD TO METAL CLAY USING THE KEUMBOO METHOD
Keum-Boo is an ancient Asian metalsmithing technique that uses heat and pressure to permanently bond specially rolled gold foil to the surface of metal, usually fine silver. The raised, crystalline structure on freshly fired metal clay, before it is burnished is ideal for accepting this layer of gold. 

1.  Create the perfect work area for Keum-Boo by setting your heat source on an oversized ceramic tile, 12” x12” or larger (or use several small tiles nested together) This will give you enough room to work and allow for a heat proof surface to set down hot tools. In addition to common sense safety precautions, like tying back long hair, setting the burner at a comfortable working height and protecting your hands and feet and eyes from flying hot metals, PROTECT YOUR CORNEAS from the heat by wearing oversized protective glasses and not hovering directly over the work area.

2. Protect your hands from the heat of the burner by wearing an inexpensive pair of leather or suede gardening gloves. Choose a pair that fits well to allow for maximum dexterity while holding tools and manipulating the gold foil.

3. Here are some heat source considerations: In addition to single or double coil electric burners (use with a fabricated steel or brass coil cover,) electric burners are also available with enclosed coils. Consider using a table top granulation kiln with special brass inserts specifically for Keum-Boo. Electric stoves can also be used. Gas stoves can be used but because they require the user to work over an open flame, the other choices are wiser and safer. When applying gold foil to extra large pieces, a jeweler’s torch might be necessary for proper bonding of the gold to the silver. When using a jeweler’s torch, increase the thickness of the gold foil used, since thin gold foil will diffuse more readily into the silver when exposed to the heat of a torch.

4.  For precise placement of Keum-Boo gold foil, position the gold foil on the project before turning on the burner. When the temperature reaches about 500°F-700°F use a burnisher to tack the gold foil in place...then go back and burnish each area.  A wood stove thermometer can be placed on top of the burner so the user will know when the proper temperature has been reached. Here are some other alternatives for gauging the proper temperature: It’s hot enough to begin tacking the gold to the silver when a toothpick or wooden shish-ka-bob skewer touched to the silver chars (Keum-Boo on Silver, Celie Fago) or when a piece of steel placed on the burner turns from yellow to brown to blue (The Complete Metalsmith, Tim McCreight)


5.  While beginners find it easier to add gold foil to the piece before the burner is turned on, experienced users are able to use a tweezers to add pieces of gold foil to the already hot metal clay piece. Some users find it easier to use a dampened paintbrush to pick up and apply the gold foil to the work. With practice, users are able to pick up a piece of gold foil with the tip of a hot stainless steel burnisher and add it to an already hot piece.

  6.  Want to add an area of gold to an already burnished and polished metal clay project using the Keum- Boo foil method? First, run the piece through a kiln cycle to remove all traces of oil and patina. This will also restore the raised, crystalline structure found on freshly fired metal clay, which is ideal for accepting a layer of gold foil.

  7. Troubleshoot these issues if the gold doesn’t bond: 1. Is the burner hot enough?  2.  Is the silver clean- free of finger prints and oils? 3. Has the gold foil made surface contact with the silver?

8.  Keep a straight pin ready for poking the gold foil in case an air pocket forms as you work.

9.  Did you know that gold can be applied to both the front and back of a project using the Keum-Boo method? Turning a side which already has the gold foil fused to it to the heat source as the other side is worked won’t hurt it.

  10.  Be creative when choosing tools for burnishing the gold foil to the silver. Standard metal and agate burnishers are perfect for no texture or low relief textured areas. Consider adapting stainless steel spoons, butter knives and forks, bending and sanding them to shape, if necessary, for areas with deeper crevices. To burnish the gold foil into deep recesses, use stainless steel ball stylus burnishers, available in various sizes (traditionally used for paper embossing.)

11.  If you find that your stainless steel burnishing tools are snagging or tearing the gold foil, lightly sand them until they are free of burs using progressively finer wet/dry polishing papers.

12.  Save every scrap of Keum-Boo gold foil and have these slivers ready to use for filling in areas that need more coverage due to a tear in the foil or movement during placement.

13. Although the gold foil can be cut as it is, it is easier to control the cut and prevent wrinkling of the foil if the foil is first sandwiched at the fold of a piece of typing paper. This method is especially important when using paper punches to cut shapes from the foil.

14. Keep paper punches sharp and lubricated by periodically punching through aluminum foil and then through wax paper, especially if you use the same punches to cut through unfired PMC sheet clay.

15.  Consider using both the negative and positive images that result when cutting the gold foil with a paper shape punch-the image itself and the outline of the image.

16.  Add a variety of scissors to your Keum-Boo tool kit. A small pair of pointy manicure scissors works wonderfully for cutting small defined shapes from the foil. A long paper shears will make it easier to cut long strips of foil. Use decorative paper-cutting scissors with scalloped or deckled edges, for example to cut the gold foil to add lots of interest to the project.

17.  Cut the gold foil with tiny circle punches (1/16th, 1/8th or 1/4th) and other small shapes of paper punches in anticipation of burnishing the foil into deeply textured areas in the silver.  A ball stylus works well for accomplishing this.  

18. Don’t confuse the 24K gold foil jewelers use for the Keum-Boo technique with gold leaf used for decorative gilding on home goods. 24K gold foil is rolled from pure gold. It requires a heat application and pressure/burnishing technique to bond it to pure silver. It’s available in several thicknesses which are all thicker than gold leaf. Gold leaf is much thinner than the gold foil used for Keum-Boo and will be absorbed into the silver when heated. Gold leaf is usually applied to any surface using sizing (gluey material) and is often a composite material (not actually pure gold)

19.  Since soldering operations like attaching pin backs or earring posts are best accomplished on metal clay pieces that have first been fully burnished to close all pores and the Keum Boo technique is best accomplished on metal clay before it has been burnished (straight from the kiln), here are some creative solutions to allow for both soldering and Keum Boo gold applications on the same piece:  Solution 1: Use a stainless steel burnishing tool to thoroughly burnish just those areas of the work where solder will be applied. Perform the soldering operation(s) and then add gold foil using the Keum-Boo method on other areas of the project. Solution 2:  Apply a slightly heavier application of gold foil to the desired areas of the project in their “fresh from the kiln” state. Burnish and then tumble the project in mixed stainless steel shot and then solder on findings or other elements. The thicker foil is necessary since some of the gold will likely diffuse into the silver during the soldering operations. Pickle as necessary.

  20.  In addition to creating a depression or two in the brass or stainless coil cover on your heat source to hold dimensional work as gold is applied, consider drilling a few holes to accommodate earring posts.

21.  Did you know that since metal clay is porous, hollow forms created with metal clay don’t need air holes to allow gasses to escape during firing? BUT, once metal clay has been fired, air holes are necessary to allow gasses to escape during other operations requiring heat, like soldering, Keum-Boo or enameling.  The air trapped inside will expand during the heating process and could cause the hollow form to explode. Prevent this by integrating air holes into your metal clay design or plan on drilling some (conspicuous or inconspicuous) after firing to prepare the work for additional processes requiring heat applications.  

22. To create different shades of gold on the same piece, apply one layer of gold in some areas, two layers of gold in other areas and so on until the contrast is evident. Kiln firing work that already has an application of gold bonded to it, will result in the gold being absorbed into the silver so it is not evident or will create a “green gold” which is not always attractive. The silver in the areas where the gold has absorbed will patina differently for some interesting effects. 

23.  Remove any marks on the gold that remain after burnishing by brushing the piece with a stainless steel brush or a soft brass brush dipped in soapy water or dampened pumice powder. This will leave a matte finish on the piece. For a high shine, tumble the work in mixed stainless steel shot and soapy water. 

24. Want to use the Keum-Boo method to add gold foil onto sterling silver? Depletion gild the sterling silver by heating and pickling it several times, until it no longer blackens. This process will raise a layer of fine silver to the surface of the metal, readying it for the Keum-Boo process.

25. Using Liver of Sulfur or another blackening agent on a project which contains both silver and gold, will greatly increase the contrast between the metals and make the gold element stand out since only the silver will take the patina.

For more in depth information on the Keum-Boo technique and the tear-away technique as they relate to metal clay, consult a copy of Keum-Boo on Silver by Celie Fago

B.  USING PMC 22K GOLD METAL CLAY
Out with the old gold and in with the new!  24K PMCGold has been discontinued in favor of a stronger, “new” 22K PMC Gold

1.  22KPMC Gold is available in 3g and 10g packages. 22K PMC Gold is 91.7% gold and 8.3% silver and has a lower firing temperature than the “old” gold.  Like the older version, 22K PMC Gold can be used alone and made into a paste. Unlike the older version, 22K PMC Gold can be kiln fired at various silver PMC+ or PMC 3 temperatures as follows: 1650F for 10 minutes, 1560F for 30 minutes, 1380F for 60 minutes or 1290 for 90 minutes. As with PMC silver, kiln firing is the preferred method for sintering lump PMC Gold Clay, but torch firing for at least two minutes at glowing red can also be used to fire PMC Gold. For conventional metalsmithing projects, fired PMC Gold can be soldered to silver using silver solder and soldered to gold using any gold solder below 22K.  On the negative side, the new PMC Gold is a dense and stiff product (like PMC3)

  2.  Add a gold element to your work with this economical “slip” tip:  Paint a layer of PMC3 silver slip onto your work in the place you would like to add a gold element and allow it to dry. Then, make a slip from a bit of PMC Gold Clay by adding a few drops of distilled water to it. Paint 3-4 or more layers of this gold slip onto your PMC piece, over the silver slip, allowing each layer of gold to dry before applying the next layer. Torch fire the piece and when it reaches the glowing stage continue to heat for 3-4 minutes. This method can be used on unfired or previously fired PMC. The key is to first apply that important layer of PMC3, silver slip underneath the layers of gold slip.

3.  Dedicate a fine detail paint brush to use for applying PMC Gold slip.  So as not to waste any gold, let the PMC Gold slip dry on the brush. It will soften back up when used to apply gold slip at your next session.

4.  To insure a good bond, secure PMC Gold lump clay with PMC silver clay in the same manner that you would use to set a fire-in-place gemstone.

5.  Some artisans prefer to add several layers of PMC Gold slip to an unfired PMC silver piece and then torch fire the work. My preferred method for adding PMC Gold slip to a project is to first kiln fire the silver piece as usual. This allows me to control the time and temperature the work is fired to. When it’s cool from the kiln firing, but not yet burnished, I add a single layer of PMC3 silver slip, followed by 3-4 layers of PMC Gold slip, drying the piece between gold applications. I then torch fire the gold onto the piece for 3 minutes.

6.  Add some gold slip to your project in places where you plan to add glass enamels. The enamel colors look much different and more vibrant over an application of PMC gold slip than they do when added over PMC silver. This is especially true for the “warm” enamel colors: reds, pinks, yellows and purple