Now that you have green finished your PMC piece, it is time to fire it. For this post, we are going to assume that you have a flat piece to fire. And we are going to talk about firing the piece in a PMC kiln.
I am going to tell you right off that I think that pieces should be kiln fired unless kiln firing will destroy the piece. That will only happen in a few cases that I won’t go into in this post. Kiln firing a PMC piece will make it stronger. You get a better firing, and a better bond. So I am a strong advocate of getting a kiln. But if you are just trying Precious Metal Clay out, find an artist in your area who has a kiln and you can usually get them to fire pieces for you for a few dollars.
If you have a PMC kiln, you can program it for different firing programs. If your piece is PMC+ or PMC3, and you did not add any gems to it, you can fire at the highest temperature and the fast setting. That means that your kiln will ramp up very fast, hold temperature for about 10 to 15 minutes, then shut off. PMC does not require a slow ramp up or down, because it is metal. Once the kiln is cool enough, you can take the piece out and quench it in cool water.
If there is a gem or glass in the piece, you cannot quench it or ramp up and down fast.
PMC can go directly on a kiln shelf. It does not need kiln wash or shelf paper, although those will not hurt the piece. PMC does not stick to a kiln shelf. It may leave a slight burn mark where the binder burned off, but it won’t damage the shelf or the PMC.
PMC+ will shrink from its green state about 10 to 15% in its fired state. It shrinks in all direction including thickness. The shortest firing is 1650 degrees for 10 minutes. You can also fire PMC3 at this temperature if it does not have glass in it, but you do not need to. It will fire at 1290 degrees for 10 minutes. The 10 minutes is the holding time, so your entire firing is about 30 minutes.
Once the Precious Metal Clay is fired, it will have a white or gray surface crust on it which you will have to clean off. More on cleaning the piece in the next post.
Here is a book that is excellent if you are interested in making beads or hollow forms from PMC: