First of all, what is PMC? PMC stands for Precious Metal Clay. PMC is one brand - ArtClay is another. And it is just what it sounds like. It's a workable clay that you fire and it becomes precious metal. I usually work with PMC silver, though I have also tried the copper clay. There are also different types. I use PMC+ because it has less shrinkage than regular PMC and it fires quickly (20 minutes at 1580 degrees).
It was invented in Japan, by Mitsubishi, originally for some other type of purpose, electronics, I think. PMC Silver is fine silver dust that has a binder added to it (some think it is simple cornstarch). You can work the clay into any shape you want, then you fire it in a kiln (or you can use a torch for some projects) and the binder burns away. Volia - you are left with fine silver. Which leads me to the next question:
What is fine silver? Fine silver is 100% silver. Most silver jewelry you see is Sterling Silver, which is an alloy of fine silver and copper. The reason you see .925 to represent sterling silver is that it is 92.5% silver and 7.5% copper. The copper adds strength. Thus, fine silver is softer and more malleable, though I've found it to be perfectly fine for jewelry. You probably would not want to use it for flatware though. : )
Recently, they introduced PMC Sterling, though I haven't tried this yet. It requires a double firing in the kiln. Honestly, I find the fine silver just fine, so I don't see the point in bothering. But if you plan to handle your jewelry a lot, you may want to opt for the sterling version.
Ok - on to the ring. The first thing to note about PMC is that it shrinks. PMC+ has a shrinkage rate of about 10-13%. It's not an exact science, which makes sizing rings very challenging. For this project, I'm actually making 2 rings, which will double my chances of getting a size 6 ring, which is what I need. I'm making one at just over a size 9, and one just under a size 9. Cross your fingers! There is also another method for doing this, that I will write about some other time. This has advantages and disadvantages.
So, first, take a big gob of PMC out of the package. Rewrap the remainder. Keep it in the plastic wrap and sealed tight or it will dry out. You don't want that.
Put some oil on your hands (I use a squirt of olive oil Pam) and rub it on your hands. This is to keep it from sticking to you and also from drying out. Massage it a bit to evenly distribute moisture throughout. Then roll it into a ball and then into a little log.
Playing cards are a great way to measure thickness. For the rings, I wanted them fairly thick so I used a thickness of 6 playing cards. I make 2 stacks and then I place another playing card in the middle that has also been sprayed lightly with Pam.
Then I take my roller (also sprayed with Pam) and roll out a strip. If you get cracks, your clay is too dry. Take a small paintbrush with water and brush your clay. Then wait a few minutes for it to absorb. You can also smooth it out with a smoothing tool.
I'm using a plastic pattern sheet to imprint a sun and stars pattern. Spray it with Pam, then rest it on top of your strip. I removed 2 cards from the stack and then lightly rolled on top of the pattern sheet to imprint it.
Then I use a plastic knife to cut the edges how I like. I don't usually make totally straight rings. I like it to look organic so I usually do some waves.
Now for the tricky part. Take your mandrel and wrap the strip around it. Since it will shrink you need to start with a bigger size. This is very cumbersome and hard to do without smudging all of your previous work. But do your best. Trim the edges where they meet in the middle and do your best to join them together using subtle force. I use a smoothing tool to clean up the seam a bit. You can also reimprint your pattern using your sheet on the seam.
I let this dry on the mandrel for a little while until it can retain its shape on its own. Put it somewhere out of the way. In the winter, I put mine on top of the running pellet stove. This dries it out really fast. If you're somewhere warm and dry, it could take a few hours. When in doubt, leave it overnight. You need it to be completely dry.
When it's dry, it will be hard to the touch. BUT IT IS FRAGILE. Be careful with it. It will easily crumble. However, if you handle it carefully, it is sturdy enough to file, and even carve. Now I take a file or some fine grit sandpaper and clean it up. Really file the seam so it's smooth and there are no sharp edges. You can also file the sides so they are straight (but again, I don't really like straight). If you're filing a lot off, capture the dust. This stuff is pricey so you don't want to waste it. You can add water and reconstitute it later to make a paste. This paste is useful in touching things up.
Ok - so at this point I'm not thrilled with either ring. They both have flaws. And usually firing doesn't magically fix them. But I still continue to hope. So now's the time to throw them in the kiln. Again, 1580 degrees for 20 minutes. It sounds quick, but it actually takes many hours to get up to the temp, and then cool off enough to open. This is the point where I usually go to bed. And so it is this time.
Tomorrow, I'll take them out, clean 'em up, measure them and hope one of them is a 6! If not, you will have the pleasure of seeing me try the OTHER METHOD. : ) Happy jewelry making!
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