Sanda Factory building in Japan

About 25 years ago, MMC developed and introduced the first metal clay. So, Precious Metal Clay is relatively new.

In the eary 90s, Mitsubishi Materials Corporation began the development of a process to make new metal clay products, known as Precious Metal Clay (PMC) which are made from micro-particles of noble metals— fine silver and gold. They won the patent for PMC on July 12, 1994 and introduced it as a commercial product within same year. Since then, scientists working at the Sanda Plant in Japan have developed clay that can be extruded, painted, and fired with a torch. Density and workability have been improved across the board, so artists today have a wide range of options to match their diverse needs. It is impossible to predict what new versions might be invented in the future, but it seems certain that they are not done yet.

PMC Timeline — the Backstory and the Products

Edited from an article in the Introduction of PMC by Tim McCreight

In August of 1994, Ron Pearson met with two men from Japan to discuss a new art material. He invited me to sit in, and the next day, two business executives laid out on his kitchen table several trays of silver jewelry that they said was made from something called Precious Metal Plasticene. They showed us a clear plastic box that held a beige-colored lump wrapped in plastic, and said that the jewelry on the table was made from this stuff.

Yeah, right.

Well, of course, now we know what they were talking about. It took about two years to bring Precious Metal Clay (yes, there was a name change) to the US market, and since then the metal clay community has seen a lot of changes. For one, a decade ago there was no such thing as a “metal clay community.” In fact, most of us remember when saying “PMC” brought only puzzled looks, and the term metal clay was nothing more than an oxymoron. Now metal clay has established a beachhead in the jewelry world, with about (check facts-two million dollars worth sold in the US last year). Jewelers, potters, and artists from many other disciplines have found in PMC a welcome companion to their other work, and a legitimate form of metalwork that provides easy access. A search on Google for “Precious Metal Clay, PMC” turns up (check facts) —750,000 entries—not bad for something that didn’t exist before 1991. Across the country and around the world, professional jewelers, craftsmen, hobbyists, and students are finding new ways to make PMC their own.

Product TimeLine

Meeting Dr. Morikawa: The Brilliance Behind PMC

By Kevin Whitmore, PMC Manager, Rio Grande

Photo of Dr. Morikawa
Dr. Morikawa, Inventor of PMC

Back in 1995 I became the precious materials product manager at Rio Grande. As a new manager, I was reading National Jeweler magazine, and ran across an article about a new jewelry making material out of Japan, Precious Metal Plasticene, invented by Dr. Morikawa of Mitsubishi Materials Corp.

By 1996, it had been renamed Precious Metal Clay (PMC) and Rio began sales to the USA.

In the summer of 2010, during the 5th PMC Conference, I finally met Dr. Morikawa. Despite all the years I've been involved in the PMC business, and despite working with many Japanese associates from Mitsubishi, I had never before had the honor of meeting Dr. Morikawa himself. Though I’d taken breakfast the first two mornings with many conference attendees, including Dr. Morikawa, I had hardly done more than say hello – constrained, as I was, by the business chatter of the others at the table and his lack of English/my lack of Japanese.

So What is PMC?

Portion of this article has been adapted from an article by Darnall Burks, published by Brynmorgen Press (date).

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 with simple, inexpensive tools to create an infinite range of forms, surfaces and textures that would be unattainable or laborious with traditional techniques. When PMC is heated to a high temperature, the organic binder burns away and the metal particles fuse, forming solid metal that can be sanded, soldered, oxidized, patinaed and polished like conventional material. Below are illustrations of the variety of particle sizes and shapes used in the different types of PMC products.

Particle size PMC
Particle size and shape in PMC®
Particle size and shape in PMC+™
Particle size and shape in PMC+™
Particle size and shape in PMC3™
Particle size and shape in PMC3™
Particle size and shape in PMC Sterling
Particle size and shape in PMC Sterling

In concept, Precious Metal Clay is an elegant and simple material. In fact, it is a highly technical product. The idea was the brainchild of a scientist named Dr. Morikawa, employee of Mitsubishi Materials Corporation in Japan. His goal was to develop a form of metal that had the feel and working properties of pottery clay. He reasoned that such a material would allow artists to create objects from silver or gold just like a potter makes ceramic items. In fact, the first PMC pieces were Japanese style tea ceremony cups formed on a potter’s wheel.

How does PMC work?

The metal clay process can be described as climbing a staircase

First, the PMC object is formed by any of a hundred different processes, including rolling, layering, imposing texture, etc. It is then set aside to dry, and we’ll call this the first step. At this point, some of the water content of the PMC leaves through natural evaporation. This will happen passively, but artists sometimes accelerate the process by using warmers or dehydrators. At this point, the PMC is tough enough to withstand sanding, carving, and light polishing.

The work is then put in a furnace, where remaining moisture is driven off—step two. The third step occurs when the temperature rises to the flash point of the binder, around 500 ̊F (260 ̊C). This creates a bit of smoke, but no more (and nothing more dangerous) than burning a pan of biscuits. At this point, the PMC is fragile because the binder that was holding the form together has been removed. There is no reason to stop the process here, so in normal uses, the work moves along to the next step.

Image magnification is 1000 times actual size.

10-minute firing
15-minute firing
20-minute firing
25-minute firing
30-minute firing

Image of the original PMC  lump clay & packaging.

How is PMC made?

The first PMC lump clay now referred to as PMC OriginalPMC® was developed and patented in the early 90s at the Mitsubishi Materials Special Products division in Sanda, Japan. Since then, many additional materials have joined this family of products. The principal ingredient in PMC is silver or gold, reduced to tiny particles smaller than 20 microns in size. These flakes are so fine that it would take as many as 25 of them clumped together to equal a grain of salt. PMC also consists of water and an organic binder. During the drying and firing process, the water and binder burn away completely and what remains can be hallmarked .999 pure silver, sterling or 22-karat gold. Dried out or unwanted PMC objects can be refined just like conventional precious metal.

The patented formula for PMC appears simple: pure water + binder + very pure silver (or gold) powder. In practice, however, several years of development went into getting the details right. The choice of binder was important. The scientists at Mitsubishi Materials chose a material often used as a food additive to assure that there would be no health risk. PMC has been tested and found to be 100% safe to handle and use.

To control shrinkage and achieve ideal workability, the amount of binder is kept to a minimum. This makes the mixing process critical to ensure that the components are distributed uniformly. The silver powder used in metal clay is very fine, finer than the finest cake flour. Further, the particle size and shape are closely controlled. The process used to make the silver powder is highly technical and a company secret. It is also an expensive process.

Are there PMC Alloys?

Most jewelry metals are alloys of silver, gold, or platinum with other metals. Sterling, for instance, is historically an alloy of 92.5% silver and 7.5% copper. Recently, alloys with other metals have been developed to make silver easier to cast, or to reduce firescale, or for other reasons. And, of course, alloys save money by diluting the expensive silver or gold with a cheaper metal. But all these other metals will oxidize in the furnace, and this prohibits proper sintering.

PMC 925 Sterling Clay
PMC OneFire 950 Sterling Clay
Many versions of silver metal clay are “fine” (that is pure) silver. This is often given the scientific designation .999, which indicates a purity of 999/1000. More recently, stronger silver clay alloy materials have been developed but they require a reduced-oxygen firing for maximum sintering strength. These alloy silver metal clays are referred to as "sterling silver" and are available in a variety of scientific destination; .925, .950, .960 which again indicates the amount of the silver contained within the alloy.

When PMC was being developed in the early 1990s, the scientists working under Dr. Morikawa made their first tests with pure gold. It was the most noble of the noble metals, and presented the most likely candidate for success. Once they had developed a formula, they moved on to silver. Pure gold PMC had excellent workability, but resulted in a metal that was too soft for practical use. In 2006, Mitsubishi scientists came full circle, using the information developed in their silver research to develop a new gold alloy. The new PMC Gold is a 22 karat alloy of 91.7% gold and 8.3% silver. This alloy has a lovely yellow color and a strength that is greater than conventional 18k gold.