Metal clay is a crafting medium consisting of very small particles of metal such as silver, gold, bronze, or copper mixed with an organic binder and water for use in making jewelry, beads and small sculptures. Originating in Japan in 1990, metal clay can be shaped just like any soft clay, by hand or using molds. After drying, the clay can be fired in a variety of ways such as in a kiln, with a handheld gas torch, or on a gas stove, depending on the type of clay and the metal in it. The binder burns away, leaving the pure sintered metal. Shrinkage of between 8% and 30% occurs (depending on the product used). Alloys such as bronze, sterling silver, and steel also are available.
Silver metal clay
Fine silver metal clay results in objects containing 99.9% pure silver, which is suitable for enameling. Lump metal clay is sold in sealed packets to keep it moist and workable. The silver versions are also available as a softer paste in a pre-filled syringe which can be used to produce extruded forms, in small jars of slip and as paper-like sheets, from which most of the moisture has been removed. Common brands of silver metal clay include Precious Metal Clay (PMC) and Art Clay Silver (ACS).
Precious Metal Clay (PMC)
PMC was developed in the early 1990s in Japan by metallurgist Masaki Morikawa. As a solid-phase sintered product of a precious metal powder used to form a precious metal article, the material consists of microscopic particles of pure silver or fine gold powder and a water-soluble, non-toxic, organic binder that burns off during firing. Success was first achieved with gold and later duplicated with silver. The PMC brand includes the following products:
- The original formula of PMC, now called "standard": fired at 900 °C (1,650 °F) for 2 hours, shrinks by 30% during firing.
- PMC+ & PMCflex: fired at 900 °C (1,650 °F) for 10 minutes or 800 °C (1,470 °F) for 30 minutes; shrinks 15%, due to a particle size reduction. PMC+ is also available in sheet form which can be worked like paper; for example, for origami.
- PMC3: fired at 599 °C (1,110 °F) for 45 minutes or 699 °C (1,290 °F) for 10 minutes; shrinks by 10%. It can also be fired using a butane torch by heating it to orange heat for at least 2 minutes. It has a longer working life than the older formulations. It is also available in slip and paste forms which can be painted onto the surface of an object to be used as a mold.
- Aura 22: a 22 k gilding material, a gold paste intended to be painted onto the surface of silver PMC pieces, or ready-made silver objects.
- PMC Pro: a harder product which is only 0.900 silver, hence it cannot be hallmarked as sterling silver. It also requires kiln firing in a tub of activated carbon for 1 hour at 760 °C (1,400 °F).
- PMC Sterling: is fired at 815 °C (1500 °F) and shrinks by 10-15%. Because of the copper content in this formula, firing is a two-step process; step one is an open-shelf firing and step two requires a firing pan with activated carbon media.
Art Clay Silver (ACS)
ACS was developed by AIDA Chemical Industries, also a Japanese company. ACS followed PMC Standard with their Art Clay Original clay (more like PMC+ than PMC Standard), which allows the user to fire with a handheld torch or on a gas hob. Owing to subtle differences in the binder and suggested firing times, this clay shrinks less than the PMC versions, approximately 8–10%.
Further developments introduced the Art Clay Slow Dry, a clay with a longer working time. Art Clay 650 and Art Clay 650 Slow Dry soon followed; both clays can be fired at 650 °C (1,202 °F), allowing the user to combine the clay with glass and sterling silver, which are affected negatively by the higher temperatures needed to fire the first generation clays. AIDA also manufacturers Oil Paste, a product used only on fired metal clay or milled fine silver, and Overlay Paste, which is designed for drawing designs on glass and porcelain.
In 2006 AIDA introduced the Art Clay Gold Paste, a more economical way to work with gold. The paste is painted onto the fired silver clay, then refired in a kiln, or with a torch or gas stove. When fired, it bonds with the silver, giving a 22ct gold accent. The same year also saw Art Clay Slow Tarnish introduced, a clay that tarnishes less rapidly than the other metal clays.
Base metal clays
Lump metal clay in bronze was introduced in 2008 by Metal Adventures Inc. and in 2009 by Prometheus. Lump metal clays in copper were introduced in 2009 by Metal Adventures Inc. and Aida. Because of the lower cost, the bronze and copper metal clays are used by artists more often than the gold and silver metal clays in the American market place. Due to Hallmarking requirements laid out in the United Kingdom, Bronze and Copper are not regarded as highly. The actual creation time of a bronze or copper piece is also far greater than that of its silver counterpart. Base metal clays, such as bronze, copper, and steel metal clays are best fired in the absence of oxygen to eliminate the oxidation of the metal by atmospheric oxygen. A means to accomplish this - to place the pieces in activated carbon inside a container - was developed by Bill Struve.
Metal clay powders
Metal clays are also available as dry powders to which water is added to hydrate and kneaded to attain a clay consistency. One advantage to the powders are their unlimited shelf life. The first silver clay in powder form was released in 2006 as Silver Smiths' Metal Clay Powder.  In the following years base metal clays by Hadar Jacobson and Goldie World released several variation containing copper, brass, and even steel.
960 Silver Alloy
Metal clay artists looking for more strength in their silver creations but without the two part firing process of working with PMC Sterling have been mixing PMC fine silver clay with equal part PMC Sterling clay.  The firing of this alloy is found to be up to 898°C (1650°F) for two hours.
- U.S. Patent 5,328,775 citing May 18, 1990 (19900518) [JP] Japan 2- 128447.
- Musante, Lynda S.; Maria Nerius (2000). Jewelry making for fun & profit. Random House Digital, Inc. p. ii-iii. ISBN 0-7615-2044-9. OCLC 410210887. Retrieved March 16, 2011.
- Introduction to Precious Metal Clay by Mary Ann Devos (C)2003 published by Wardell Publications Inc ISBN 0-919985-36-X
- McCreight, Tim. "What's New?" Metalsmith Spring 2006, Vol. 26 Issue 1, p42-45, 4p
- Metal Clay Artist Magazine 1 (3): 7 Missing or empty
- Art Jewelry, July 2008: 30 Missing or empty
- MCPsilver999 | url=http://www.metalclaypowder.com |
- 960: A new alloy of sterling PMC |url=http://celiefagojewelry.blogspot.com/2014/02/960-new-alloy-of-sterling-pmc.html