A new substance called Precious Metal Clay has opened new horizons for glassworkers as well as for metalworkers. This product, developed in Japan and available in America from Rio Grande, is not actually clay at all but particles of fine silver suspended in an organic binder that feels rather like porcelain clay. It can be worked like clay, but when fired in a kiln at 1650 degrees for two hours the organic binder burns off and the silver particles sinter together, leaving a piece of fine silver - purer and more tarnish-resistant than sterling. By a happy coincidence, fine silver is one of the metals recommended for using with fused glass - it can withstand the temperatures required for fusing and does not develop fire scale as sterling silver does.
Although it can be worked like clay, the price of PMC (about $30/oz.) precludes a lot of traditional ceramic techniques. You're probably not going to see many PMC vases or large sculptures. However, it's wonderful for making small castings for jewelry and beads.
Here I'm going to be demonstrating just one of many uses; how I use PMC to create very detailed silver images fused into my glass beads.

The first step is making the mold. I like Creative Paperclay for the mold material; it's cheap, dries fast, and withstands the high temperatures of sintering without giving off toxic fumes or crumbling in the kiln. I roll out a thin slab of paperclay and press something into it - a handmade stamp, a commercial stamp, a sprig from a bush, a charm, whatever I wish to recreate. Whatever you use needs to be deep enough to create a clear impression in the paperclay.

After making the impression, I put the paperclay mold away to dry for 24 hours. (It might dry faster in a less humid climate; that's what it needs here in Austin.)

The next day, I work a pinch of PMC into the mold, pressing it down firmly to make sure it fills all the crevices. Then I use a tissue slicing blade (available from medical supply stores, though they may wonder why you want something that's normally used to do autopsies) to gently slice away any excess PMC from the top of the mold. Here you see a shape made from a tree stamp that I cut myself. The stamp is thick and not too detailed, so it's relatively easy to make a PMC piece from it.

Once I've filled enough molds to fill my kiln, I set them all on a kiln shelf and fire. The firing process is relatively simple: you just go up to 1650 degrees as fast as you can and hold it there for two hours. It is important to maintain the correct temperature. Too low, and your PMC won't sinter completely, leaving you with a brittle piece. Too high, and the silver will convert itself into a shapeless blob. I've fired PMC by sitting over the kiln and twiddling the infinite control switch for two hours, and I've done it with a kiln controller. A kiln controller is an expensive piece of equipment, but it looks a lot less expensive after a few PMC firing sessions!

When the firing is done, you can pick up the piece with tongs and drop it into water if you're impatient to see results right away, or you can just open the kiln lid and wait until the pieces are cool enough to handle. I prefer the second method, because I've found that frequently the paperclay mold remains strong enough to be used again in a second firing if I handle it gently at this stage.

It should be possible to gently peel the metal piece away from the mold at this point. If you have a very detailed mold with undercuts, you'll need to crumble it away from the metal, and bits of paperclay may remain stuck to the silver. These can be cleaned off with a steel brush, though I prefer not to work the silver too vigorously at this stage because the thin pieces I make with this technique are quite fragile until they are fused into and supported by the glass.

As you can see, the silver piece isn't too attractive at this stage: it has a dull white matte surface, doesn't look like silver at all. In "traditional" PMC work, if there's such a thing as tradition in this new field, you would now clean up the silver to get rid of the white surface and burnish it to bring out the shine. However, I don't do this now, because I know the piece is going to go back in the kiln for at least one more firing, possibly two, and I'd just have to clean and burnish it all over again after each firing.

The next step is to lay up a glass "sandwich" just as I would for any fused bead, with fiber paper creating a channel between the layers of glass. I use a little white glue to adhere the silver piece to the top of this sandwich, because I'm probably going to flip the whole thing upside down before the next firing (so that the weight of the glass will help it adhere to the silver).

Now I fire the glass and silver together, taking it slowly up to fusing temperature and holding for a little longer than I do for a "normal" full fuse. (Exact temperatures and times here depend on your kiln.) Afterwards the pieces have to cool slowly, as with any fusing.

Depending on the color of glass you use, the silver may have reacted chemically with the colorants used in the glass to change the colors of the finished piece. Here you can see the typical swirling patterns created by this reaction. When I want this sort of effect, I fuse the silver directly into the colored glass; when I have colors or patterns in the unfired glass that I want to maintain unchanged, I lay a piece of thin clear glass over them and fuse the silver into that.

Depending on how the piece came out of fusing and the effect I want, I may cold work the glass now and put it back in to fire polish. This won't hurt the silver, but again, there is absolutely no point in cleaning up the silver surface until you are completely through with all firings.

Once that happy stage has been reached, you can moisten the top of the piece with a drop of detergent for lubrication and scrub it vigorously with a steel-bristled brush to remove the white coating. This should leave you with a matte but silver-colored surface. I don't have a picture of the tree piece at this stage, but here are snapshots of some others from the same firing. The hand was made from a hand-shaped bead, the plant image from a sprig of rosemary, and the leaf that you can just see in the bottom lefthand corner came from a commercial stamp.

Finally, you can burnish the metal to bring out the shine of the silver. With some complex images I finish the work off by partially oxidizing the silver to bring out the pattern, but usually I leave it alone after burnishing.