Precious Metal Clay — Sintered Silver and Gold from a Mouldable Putty
Precious Metal Clay — Sintered Silver and Gold from a Mouldable Putty
A 1990s Mitsubishi Materials development that turned fine metal powder into a clay-form medium for studio jewellers
Precious metal clay (PMC) is a mouldable composite of fine precious-metal powder — silver, gold, platinum, copper, or bronze, depending on formulation — suspended in an organic binder and water that handles like potter's clay during forming and yields nearly pure sintered metal after firing in a kiln or with a torch. The material was developed by Mitsubishi Materials in Japan in the early 1990s, originally as a means of recovering precious metals from electronics manufacturing waste, and was launched as a craft product in 1995. PMC and its principal competitor, Art Clay (developed by Aida Chemical Industries), have transformed studio and hobby jewellery making by allowing complex forms to be produced without traditional metalsmithing equipment.
Composition and firing
The original Standard PMC and Art Clay Standard formulations contained roughly 90 percent fine silver powder by weight, with the balance made up of an organic cellulose binder, surfactants, and water. After shaping and drying the binder is removed by combustion during firing, and the metal particles sinter — fuse at points of contact through diffusion at temperatures below the bulk melting point — into a coherent solid. Standard silver PMC fires at approximately 900 degrees Celsius for two hours and shrinks roughly 28 to 30 percent in linear dimension during firing.
Subsequent generations of the product have reduced shrinkage and improved properties. PMC+ and Art Clay 650 fire at 650 to 900 degrees Celsius with shrinkage around 12 to 15 percent. PMC3 and Art Clay 650 Slow fire as low as 600 degrees Celsius. PMC Pro and other newer formulations contain higher metal loadings (95-99 percent fine silver) for further reduced shrinkage and improved as-fired density. Gold PMC formulations fire at 800 to 900 degrees Celsius and produce 22 carat gold (916 fine) after sintering. Platinum PMC requires higher firing temperatures (1100-1300 degrees Celsius) and is the most demanding to work.
Firing options range from professional kiln (the standard for production work, providing controlled temperature and time profiles) to butane torch (acceptable for small silver pieces) and even gas hob (with appropriate stainless steel mesh and ventilation, suitable for small Standard or PMC3 pieces). Each firing method has documented protocols and material-specific limitations.
Working properties
In the unfired clay state, PMC handles broadly like polymer clay or fine ceramic clay. It can be rolled to sheet, extruded through pasta-machine-style rollers, formed in moulds, carved, embossed, textured by impressing leaves or fabric or rubber stamps, and joined to itself simply by moistening the surfaces. Drying takes minutes with a hairdryer or hours at room temperature. Once dried but before firing, the material can be sanded, drilled, and finely carved with standard tools — a stage often called "greenware," using ceramicist terminology.
The fired metal is the same material as conventionally produced fine silver, gold, or platinum at the corresponding fineness, with comparable mechanical properties. Some early generations of PMC produced slightly more porous fired metal than cast or wrought equivalents, with implications for stone-setting and structural integrity at thin sections; the newer high-loading formulations approach the density of cast metal.
In the trade
PMC and Art Clay have established a substantial studio and hobby market, with certified instructor networks (the PMC Guild internationally, Art Clay Society chapters), specialist retailers, and dedicated craft publications. Production jewellers working at the bench-and-scale of one-of-a-kind and small-batch designs use PMC for filigree, fine sculptural work, organic textures, and rapid prototyping. The material has not displaced traditional metalsmithing in commercial production at scale — material costs and the firing-shrinkage variable make it less efficient for repeat production than cast or fabricated work — but for studio and small-batch jewellers, the access it provides to fine silver and 22 carat gold without the equipment investment of full traditional metalsmithing has been transformative.
Buyers of PMC pieces should be aware that the material, when properly fired, is genuine fine silver or 22 carat gold and carries the corresponding hallmark eligibility — UK PMC pieces above the hallmarking threshold are submitted to the assay office in the same way as conventionally produced fine silver. The presence of a hallmark on a PMC piece confirms metal fineness regardless of forming method.
Care
Fine silver (999) PMC tarnishes more slowly than sterling (925) silver because it contains no copper, but it is also softer and shows wear more readily. PMC pieces benefit from the same care as any fine silver: storage in anti-tarnish environments, gentle cleaning with a polishing cloth, and avoidance of harsh chemicals. Gold PMC at 22 carat is similarly soft compared to common 18 carat alloy and benefits from protected settings for stone work.