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Precious Metal

By Jeanette Landenwitch, via Gem Cutter News, 12/08

Introduction

PMC is a revolutionary development in the precious metal industry. It allows for easy creation of detail in designs that would be very difficult and painstaking to achieve using conventional forms of metal and methods of working. Expensive tools and equipment are not needed to work with PMC.

It is a very versatile product. The silver and gold PMC can be used separately, or in combination with each other, as in two-tone pieces. PMC can be combined, before firing, with other materials such as potter's clay, sterling silver, high-fired ceramics, synthetic corundum stones, and, after firing, using epoxy, or soldering methods. It can be enameled, carved, or even wheel-thrown. Three dimensional pieces and hollow forms such as beads and vases can easily be made.

PMC is a very 'forgiving' medium. Changes in the piece can be made at any stage of creation, allowing for the design to truly evolve. New designs can be tested with very little time commitment. You will also learn that, with a little vigilance, there is virtually no wasted PMC. Slightly or completely dried PMC can be re-hydrated to working consistency, or made into slip (a paste form of PMC used for joining and repairing).

PMC has incredible potential and limitless possibilities. Your designs can be as simple or as intricate as you desire. As you learn about PMC, your imagination will be more than sparked. You will find yourself thinking of more design ideas than you have time to create. By all means try new things and experiment with new ideas. This is a product that is in its infancy. It has tremendous potential and is very easily individualized. Experienced artisans, jewelers, clay workers, bead-makers, etc., will find ways to incorporate PMC into existing methods of working. Novice hobbyists and budding artisans will have wonderful success from the very beginning. You will find great satisfaction and encouragement when you see the professional results you can achieve.

Those who experiences PMC will add a dimension to their work that has been unavailable until now.

Properties of Standard PMC, PMC+, and PMC 3

Precious Metal Clay is available in pure silver, and in 24 Karat gold and the just released PMC Bronze. We'll only discuss the silver and gold here.

There are three types of silver PMC-standard PMC, PMC+ (called PMC Plus), and PMC 3. Each can be worked the same, using the same tools, yet each type also has its own properties and characteristics. These varying qualities are what make using PMC so very versatile. Although each type of silver PMC has its own rate of shrinkage, the shrinkage is uniform throughout the piece. Therefore, the proportion and scale within the piece before it is fired, will remain the same after firing, the piece will just be smaller. Also note that the shrinkage will occur in all directions- length, width, and thickness. One of the beauties of the shrinkage characteristic is that you create the piece in a larger size (definitely a plus for those of us who wear glasses), and the detail becomes more enhanced after it has been fired.

Standard PMC

In standard PMC, whether silver or gold, the binder is about 30% of the content of the silver clay mixture. Since the binder burns away, the piece will be about 70% of the original size after firing. There is a PMC ruler made specifically to help measure the shrinkage of standard PMC. I have found it to be very accurate. This ruler works for standard PMC only, both silver and gold. Each side has a true 6" ruler. On one side there is also an expanded ruler that shows the size the piece should be made before firing in order to achieve the intended finished size. For example, if you want a piece to be 1" long when it is finished, then you would use the expanded ruler and actually make the piece the expanded 1". On the reverse side there is a shrunken ruler. If you are using a mold, for instance, that the size has already been determined, then you would measure that mold with the true 6" ruler and check the shrunken ruler to see what the actual after firing size would be. So, a piece made from a 1" mold before firing would actually end up being less after it is fired.

Standard silver PMC is fired at 1650F for two hours. Gold is fired at 1830F for two hours. After firing, PMC is stronger than the same item made in conventional metal of the same purity. PMC is more porous, therefore resulting in pieces that are lighter in weight than their counterparts in conventional fine silver and 24K gold. This characteristic is particularly advantageous when making larger wearable art items.

PMC+

Silver PMC+ has approximately 12% binder in the content of the clay, and therefore shrinks to about 88% of its original size. It is denser after firing than standard PMC, therefore is slightly heavier. There are three firing temperature and time options for PMC+. It only needs to be fired for 10 minutes, but can be fired longer. When fired for two hours, at 1650F, it becomes almost as strong as sterling silver. Firing at the lower temperature of 1470F makes it possible to embed sterling silver findings, such as earring posts, before firing.

PMC 3

Silver PMC 3 has the same shrinkage rate as PMC+. PMC 3 can also be fired for as little as 10 minutes, or as long as two hours. If fired for two hours it will become slightly denser than the other two forms of PMC, and, therefore, slightly stronger. If fired for two hours, PMC 3 must first be heated to about 250C for at least 10 minutes to be sure the binder burns away.

No matter which form of PMC you use, after firing it is pure precious metal and can be handled as such. It can be sanded, soldered, polished, tumbled, burnished, oxidized, wire brushed for a satin finish, enameled, etc.