Metal clays are a remarkable craft innovation combining clay sculpting and metal working, allowing an artisan to create works of real metal using the techniques of clay modeling. While experience and skill in clay sculpting is transferable to working with art clay, a number of processes and techniques are specific to this type of clay.
Sculpting
Metal clay is a form of air-dry clay made with water, metal dust and powdered organic material. Sculpting with it is quite similar to sculpting with other air-dry clays. The clay is water-soluble and can be softened with water if it starts to stiffen, so keep a small dish of water on hand.
Before you start to work with the clay, you should condition it by kneading it thoroughly and, if necessary, working in a few more drops of water. This will make the clay more malleable.
If you find that the clay is leaving too much residue on your hands, tools or work surface, you can use a small amount of cooking oil to keep it from sticking. Be careful, though. Too much oil will ruin the clay's adhesion. Use just enough to make your hands feel a little oily, but not enough to make them shiny.
As you're sculpting, bear in mind that your piece will shrink slightly as it dries. For the most part, this isn't particularly noticeable except in the case of rings. Rings should be made about a size and a half larger than you intend them to end up.
Drying and Sanding
Your metal clay piece must be fully dry and hardened before you fire it or cracking might occur. Drying time will depend on the size and shape of your piece, but pieces smaller than your palm will usually be fully dry after 24 hours. With large pieces, wait two days. If you want to be extra sure about a piece, or get it dry faster, bake it in a conventional or toaster oven at about 150 to 200 degrees Fahrenheit. If your piece is large or thick, bear in mind that just because the outside is dry doesn't mean the inside is.
Once your piece is dry, you'll want to sand and file it to make it as smooth as possible. Remember that whatever texture your piece has before you fire it is the texture it will have in metal after firing.
Firing
Bronze and gold clays can only be fired in a kiln, while silver clay can be fired in a kiln or by hand using a creme brulee torch.
For kiln-firing, use a kiln suitable for low-fire ceramic clays. You'll want to know exactly how hot your kiln gets and to check the manufacturer's instructions for the particular silver clay you're using to make sure you're in the right temperature range and to make sure you fire for the right amount of time. This can vary between types and brands of metal clay, and if you don't fire the clay hot enough or long enough, it could crack.
When firing silver clay with a hand torch, place the clay item on a firing brick (these are often sold where metal clays are available) or use a regular concrete brick. Fire the clay in the torch's flame until the entire piece (or the portion you're firing, if the piece is large) until the clay glows evenly peachy-orange. Let the piece burn at this temperature for at least several seconds, but less than a minute. If you see the surface of the glowing metal starting to appear metallic and shiny, stop firing because that means the metal itself is starting to melt and your piece could lose its shape. Allow the piece to cool for at least a half hour before handling.
Brushing and Burnishing
Once your fired piece has fully cooled, it's time to brush and burnish it. First, brush your piece thoroughly with a stiff-bristled wire brush. This will remove the traces of ash and burnt organic powder, leaving only metal and allowing it to shine.
After brushing, wash away the remaining dust with water, then burnish your piece. Burnishing consists of rubbing the surface of the metal with a smooth, pointy-tipped tool made either of agate or metal. This compresses the metal fragments, making them smoother and much shinier.
If you don't have a burnishing tool, you can burnish your piece using a piece of tumbled agate, quartz, amethyst, or anything else that's smooth and hard. Without a pointy tip, it will be difficult to burnish detail work, but this method works well enough on large or flat surfaces.
