Silver metal clay offers an incredible gateway into the world of metal jewelry creation. Its unique properties allow artists to sculpt, texture, and shape designs with the ease of clay, which then transform into solid, sintered metal after firing. While the luminous beauty of fine silver is captivating on its own, imagine adding the rich, warm glow of pure gold accents. This isn’t about plating or flimsy leaf; it’s about an ancient, permanent bonding technique known as Keum-Boo.
Unveiling the Magic of Keum-Boo
Keum-Boo, translating literally to “attached gold” in Korean, is a traditional metalsmithing technique with roots stretching back centuries. It involves permanently bonding thin sheets of pure (24 karat) or high-karat (usually 22K) gold foil onto a silver surface using heat and pressure. It’s a process distinct from gold plating, which uses electrochemistry, or gilding with gold leaf, which relies on adhesives and is far less durable for wearable art. Keum-Boo creates a molecular diffusion bond – the gold and silver atoms literally intermingle at the surface when heated, forming a lasting connection that won’t easily peel or flake off.
Historically applied to depletion-gilded sterling silver or fine silver, Keum-Boo has found a perfect modern partner in fired silver metal clay. Why? Because most silver metal clays, after firing according to the manufacturer’s instructions, result in a piece that is nearly pure fine silver (99.9% silver). This is ideal for Keum-Boo.
Why Fine Silver from Metal Clay is Perfect
Traditional Keum-Boo on sterling silver (92.5% silver, 7.5% copper) requires an extra step called depletion gilding. This involves repeatedly heating and pickling the sterling silver to bring a layer of fine silver to the surface, as the copper content in sterling interferes with the bonding process. Fired silver metal clay, being inherently fine silver, bypasses this requirement entirely. You work directly onto the sintered fine silver surface, making the process considerably more straightforward for home studio artists and metal clay enthusiasts.
The fine silver surface readily accepts the gold foil when the correct temperature and pressure are applied. This accessibility opens up a world of design possibilities, allowing creators to add luxurious gold elements without needing complex electroplating setups or dealing with the intricacies of preparing sterling silver.
The Keum-Boo Application Process on Silver Clay
While the principle is simple – heat and pressure – achieving beautiful, durable results requires attention to detail. Here’s a breakdown of the typical steps involved when applying Keum-Boo to a fired silver metal clay piece:
1. Preparing Your Fired Silver Piece
Your journey begins after your silver clay piece has been successfully fired and initially cleaned. The surface where you intend to apply the gold must be meticulously prepared. It needs to be:
- Clean: Free from any oils, fingerprints, polishing compounds, or oxidation. Wiping with alcohol or acetone on a lint-free cloth is a good final step.
- Smooth (or Textured as Desired): While Keum-Boo can follow textures, the actual bonding points need good contact. For a bright gold finish, the underlying silver should ideally be burnished to a high shine before applying the gold. Use a steel or agate burnisher. If you want a matte gold look, you can apply it to a well-sanded (e.g., 600-grit or finer) or wire-brushed surface, but ensure it’s perfectly clean.
- Dry: Any moisture will interfere with heating and bonding.
Think of it like preparing a canvas; the better the preparation, the better the final artwork. Any imperfections or dirt on the silver can prevent the gold from bonding properly.
2. Preparing the Gold Foil
You must use 24K or 22K gold foil specifically intended for Keum-Boo. It’s significantly thicker and more robust than gold leaf used for gilding. Gold leaf is simply too thin and fragile; it will likely disintegrate under the heat and pressure and won’t form a proper diffusion bond. Keum-Boo foil is typically sold in small sheets. Carefully cut the foil into the shapes you desire using a sharp craft knife or small, sharp scissors on a clean surface like glass or a plastic sheet. Small, intricate shapes can be challenging, so start with simpler forms if you’re new to the technique. Tweezers are essential for handling the delicate foil pieces.
Important: Always use 22K or, ideally, 24K gold foil specifically sold for Keum-Boo. Do not attempt this technique with standard gold leaf meant for gilding, as it is too thin and lacks the integrity to bond correctly under heat and pressure. Using the wrong material will lead to frustration and failed results.
3. Heating the Silver
The silver piece needs to be heated to a specific temperature range, typically between 500°F and 750°F (approximately 260°C to 400°C). The exact temperature depends on your setup and the specific piece, but it needs to be hot enough for diffusion to occur but *below* the melting point of silver. Common heating methods include:
- Electric Hot Plate: A popular and relatively controlled method. Place the silver piece directly onto the preheated surface.
- Torch Heating: You can heat the piece from below or gently from above with a jeweler’s torch. This requires more practice to maintain an even temperature and avoid overheating or melting the silver.
- Kiln: Some artists use a digitally controlled kiln set to the target temperature.
Gauging the temperature often involves observation. Some artists look for a slight darkening or specific heat haze around the piece. Temperature indicator crayons or drops can also be used, but experience is often the best guide. Consistent, even heat is key.
4. Applying and Burnishing the Gold Foil
This is where the magic happens! Once the silver piece is at the correct temperature:
- Placement: Using clean tweezers, carefully place a piece of cut gold foil onto the hot silver surface precisely where you want it.
- Initial Tack: Gently press the foil down with a non-marring tool (like a wooden stick or the smooth end of an agate burnisher) to tack it in place briefly.
- Burnishing: Immediately and firmly burnish the gold foil onto the silver using a highly polished steel or agate burnisher. Use smooth, overlapping strokes with consistent pressure. The goal is to press the gold into intimate contact with the hot silver, initiating the diffusion bond. You should see the gold conform to the silver surface and potentially change slightly in appearance as it bonds. Work quickly but methodically.
If the piece cools too much, the bond won’t form. If it’s too hot, the silver could be damaged, or the gold might behave unexpectedly. If the foil doesn’t stick, the silver likely wasn’t hot enough or clean enough, or your burnishing pressure wasn’t adequate.
5. Building Layers and Finishing
You can apply multiple pieces of foil, either adjacent to each other or slightly overlapping, during the same heating cycle or by reheating the piece. Once all the gold is applied and the piece has cooled, give it a final, thorough burnishing (cold) with your agate or steel burnisher. This smooths the gold further, hardens it slightly, and brings out its maximum shine. Be careful not to burnish so aggressively that you scratch or thin the gold layer excessively.
After Keum-Boo, the piece can be further finished. Tumbling with steel shot can brighten both the silver and the gold, but protect intricate gold details if necessary. A patina (like Liver of Sulfur) can be applied to the silver to create a dramatic contrast with the bright gold accents, making them pop even more.
Essential Tools and Materials Summary
- Fired, cleaned fine silver metal clay piece
- 22K or 24K Keum-Boo gold foil (NOT gold leaf)
- Heat source (hot plate, torch, or kiln)
- Agate and/or highly polished steel burnisher(s)
- Fine-pointed tweezers (non-magnetic stainless steel preferred)
- Sharp craft knife or scissors
- Clean cutting surface (glass, plastic sheet)
- Heat-proof work surface
- Safety glasses
- Optional: Heat-resistant gloves, temperature indicator, third hand
Tips for Keum-Boo Success on Metal Clay
Cleanliness is Paramount: Repeat it like a mantra. Any grease or dirt will block the bond. Clean your tools, your hands, your work surface, and especially the silver piece itself.
Master Temperature Control: This is often the trickiest part. Too cool, no bond. Too hot, potential damage. Experiment with your heat source on test pieces to find the sweet spot.
Burnish Thoroughly: Don’t be timid with the burnisher once the foil is placed on the hot silver. Firm, consistent pressure is needed to ensure metal-to-metal contact for bonding.
Start Simple: Begin with applying simple gold shapes to flat or gently curved surfaces before tackling complex patterns or heavily textured pieces.
Foil Handling: Keum-Boo foil is delicate. Handle it carefully with tweezers to avoid wrinkles or tears. Static electricity can be an issue; working on a slightly humid day or using anti-static tools can sometimes help.
Endless Creative Horizons
Keum-Boo isn’t just a technique; it’s an enhancement that elevates silver metal clay work. Imagine delicate gold veins running through a textured silver pendant, a bold geometric gold pattern on sleek silver earrings, or tiny 24K gold “dewdrops” accenting a floral silver design. You can mask areas, layer foil pieces, or combine Keum-Boo with patinas, gemstones, or even other metal clays.
The contrast between the cool white of fine silver and the rich yellow of high-karat gold is timeless and visually stunning. Keum-Boo allows metal clay artists to achieve this sophisticated look with a process that, while requiring practice, is far more accessible than many other gold application methods.
Adding Keum-Boo to your metal clay skill set opens up a new dimension of design. It’s a bridge between ancient tradition and modern materials, offering a way to imbue your silver creations with the unmistakable warmth and luxury of gold. Don’t be intimidated – gather your materials, prioritize safety and cleanliness, practice your heating and burnishing, and start experimenting with adding golden touches to your silver metal clay art.
