Working with Metal Clay

March 29, 2020
Working with metal clay

An Introduction to the Material, Tools and Techniques of Working with Precious Metal Clay

What is PMC?

Precious Metal Clay represents a dramatic development in the handling of precious metals. PMC consists of microscopic particles of silver or gold suspended in an organic binder to create a pliable material with a consistency similar to modeling clay. PMC can be worked with the fingers and simple inexpensive tools to create a vast range of forms and surfaces that would be unattainable or laborious with traditional techniques.

When heated to a high temperature, the binder burns away and the metal particles fuse to form solid metal that can be sanded, soldered, colored and polished like conventional material. This booklet describes some of the techniques devised for PMC and will guide you through your first firing experience.

History

Precious Metal Clay was developed by scientists working at the Mitsubishi Materials Special Products division in Sanda, Japan. After years of experimentation the first patents were awarded in the early 1990s with many additional materials joining the family of products. The principle ingredient of PMC is gold or silver, reduced to tiny flakes smaller than 20 microns in size. As a point of reference, it would take as many as 25 of these particles clumped together to equal a grain of salt.

The other ingredients in PMC are water and an organic (naturally occuring) binder. After firing, the water and binder have completely burned away so what remains can be hallmarked as .999 silver or gold.Dried out or unwanted objects can be refined just like conventional precious metal.

How Does It Work?

Under the proper conditions, crystals of metal fuse together in the same way that droplets of water run together to make larger puddles on the window pane. In the case of metals, oxides (tarnish) that form naturally on most metals prevent this from happening. The solution here is to use precious or noble metals in their pure state. These do not readily oxidize so even at the high temperatures needed to induce fusion they remain free of coatings. This explains why there is not a brass or sterling version of PMC - short of firing in a vacuum it won't work.

Form

Using very simple tools and your own very talented fingers, PMC is rolled, pressed, squeezed, layered and molded into a desired shape. Parts can be added, removed and refined as you go, making this a spontaneous and liberating process.

Fire

After it has dried, the PMC object is taken to a specific heat (as described on page 9). This drives off whatever moisture remains, then burns the binder. This goes off as a harmless smoke. At this point the PMC is a fragile porous metallic husk. At higher temperatures the particles melt into one another to form a solid dense metal. Depending on the type of PMC, this can take from 10 minutes to two hours.

Finish

After firing, the object can be handled like any other gold or silver item. It can be soldered, burnished, buffed, tumbled, plated, etc. to achieve whatever finish you want.

Three Kinds of PMC&ldots;

The Original! This version has the best working properties and remains moist a bit longer than the others. It shrinks 28%, so textures and details are enhanced after firing. Objects made on original PMC remain slightly porous even after proper firing. This means they are lighter than the same size object made of wrought silver, but also means strength is reduced.

This version, called "PMC Plus" is made of a differently shaped metal particle and contains less binder. The shrinkage rate is 12-15%. PMC+ offers three distinct firing options, two of them at lower temperatures than the original. Objects made of PMC+ can...

Source: www.silversmithing.com
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