Basics of Precious Metal Clay
by Laurie Union
Precious Metal Clay Mitsubishi Materials is the first manufacturer of Precious Metal Clay. Later Aida Chemical Industries created Art Clay. Both clays have some comparable properties however the clay’s sinter temperatures and times are important to note. Here is a list of the current known firing temperatures for proper sintering for PMC.
Fine Silver: PMC Original, PMC+ and PMC3
PMC Original has the highest shrinkage rate and can shrink as much as 28-30%. The firing temperature is 1650◦ F for at least 2 hours. Rationale: the molecule size varies a lot and some are large so in order to get complete sintering, the firing temp and time are high and long respectively. This clay has the longest working time and is great for pieces you particularly want to shrink. Often the natural form of something you are creating can be large and in the use case of this clay, you get such a natural shrinkage that it is perfect for these occasions.
PMC+ was created to incorporate gemstones that have to fired at lower temperatures. The molecular size has now come down to smaller circular silver particles surround by binder and more uniform in size. Shrinkage is advertised to be 10-12%. The general firing temperature can be lower than PMC Original to accommodate gems. I find PMC+ to be the easiest clay to work with for both longer working time and less shrinkage than original with a more predictable shrinkage. PMC+ has the following recommended firing schedule:
1650◦ F for at least 10 minutes 1560◦ F for at least 20 minutes 1470◦ F for at least 30 Minutes
PMC3 was created for strength and to incorporate gemstones that require lower firing temperatures. Shrinkage is advertised to be 8-10%. The molecule size is much smaller and more uniform than PMC Original and PMC+. PMC3 has a very short working time but is very strong and the recommendation if making rings/bracelets is to use this clay for strength.
1290◦F for at least 10 minutes 1200◦ F for at least 20 minutes 1110◦ F for at least 30 minutes
PMC Original, PMC + and PMC3 can all be fired up to 1650 for 2 hours. What is new in the world of Silver PMC? PMC PRO
PMC PRO is a new type of precious metal clay from Mitsubishi Materials. This clay is 90% silver and 10% copper and therefore is very strong and can be forged like Sterling Silver. As Sterling silver also oxidizes, this clay has similar behaviors and if fired in activated carbon, can be fairly
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clean if you let the container and carbon cool down before removing from the kiln. This clay’s MOHs hardness is double PMC3’s hardness. It is the hardest silver metal clay and can be made into nails and hammered without any cracks or breaking. Since it has other metals, it must be fired in activated carbon keeping out oxygen. The possibilities are now endless– we can now fire diamonds in clay using this clay – PMC Pro! There are many early reports on firing temperature and time and I will just list one here but please read as the material becomes more mature, variations to this schedule will probably be published in the future.
Firing temperature is about 1400◦F for at minimum of an hour. Shrinkage will be determined where in the carbon the piece sits. 1 the shrinkage rate varies a little bit so the range found so far is 15-20% depending on how far in to the activated carbon the piece sits, size of piece and sinter time.