PMC Pro is a sterling-silver metal clay manufactured by Mitsubishi Materials Corporation under the Precious Metal Clay brand, introduced to give studio jewellers a 925-fineness alternative to the fine-silver clays that dominated the early generation of metal-clay materials. Like all metal clays, PMC Pro consists of fine metal particles bound in an organic matrix that burns off during firing, leaving a sintered metal article with the form set in the clay state.

Composition and firing

The fired alloy contains 92.5 percent silver and 7.5 percent copper, the standard sterling composition. The presence of copper changes the firing chemistry: where fine-silver clays sinter cleanly in air, copper oxidises during heating and the oxide layer disrupts particle bonding. PMC Pro must be fired in activated carbon to prevent this oxidation. The work is buried in granular activated carbon inside a kiln vessel, the carbon consumes available oxygen as it is heated, and the resulting reducing atmosphere lets the silver-copper particles sinter without copper-oxide contamination.

Recommended firing schedules approximate two hours at 900 degrees Celsius. Lower temperatures yield incomplete sintering with reduced strength; higher temperatures risk slumping and grain coarsening. Properly fired, the resulting metal is solid sterling silver with mechanical properties similar to mill-rolled sterling, suitable for structural elements that fine-silver clay cannot reliably support.

Working properties

Unfired PMC Pro handles much like other metal clays — extrudable, mouldable, carvable when leather-hard, sandable when fully dry. Shrinkage during firing is approximately 15 to 20 percent, comparable to other PMC variants and slightly less than some fine-silver formulations. The fired surface accepts standard silversmithing finishing operations including hammering, soldering, polishing, and oxidation patinas; the alloy responds to work hardening as solid sterling does.

The material is sold by weight in lump and syringe forms. Studio jewellers use it for elements that need the strength and traditional colour of sterling — bezel cups, ring shanks, hinged components — while reserving fine-silver clay for filigree, surface texture, and applications where pure-silver colour is preferred.

Position in the metal-clay market

PMC Pro competes with Aida Chemical's Art Clay sterling formulations and with bronze and copper clays serving the same functional niche of structurally robust fired metal. Within the PMC family, it occupies the structural-sterling slot alongside fine-silver PMC Plus and PMC3 (which sinter in open-air kilns) and the gold and palladium clays in the broader product line. The need for carbon firing makes PMC Pro slightly more involved to use than open-air clays, and studio jewellers select it specifically when the strength and colour of sterling justify the additional setup.

In the trade

Buyers of finished PMC Pro work are purchasing sterling silver to the standard 925 fineness; assay should confirm the alloy when the work is presented for trade. Studio markings, kiln-firing provenance, and maker reputation are the relevant assurances; the metal-clay origin does not affect the sterling status of the finished piece. Pieces that combine PMC Pro structural elements with fine-silver decorative elements are increasingly common and should be marked according to the lower fineness if the two are joined inseparably.

Further reading

• GIA Gems & Gemology — silver alloys and metalwork articles
• International Gem Society — sterling silver and alloys reference
• American Gem Trade Association — silver standards in the trade