Professional Jeweler Archive: Stone-In Platinum Casting

May 2000

Precious Metals & Bench: Metalsmithing


Stone-In Platinum Casting

Quick-setting investment originally designed for dentists allows bench jewelers to sink their teeth into casting platinum with diamonds


Marc Robinson, a hydrometallurgist, has discovered things about platinum casting investments he says will forever change the way bench jewelers and manufacturers think about the process. Robinson is COO of Precious Metals West/Fine Gold, a Los Angeles manufacturer of gold, silver and platinum solders, alloys, sheet and wire products.

Robinson developed a formula using quick-setting investment designed for the dental industry that allowed him to perform the first successful stone-in platinum casting with diamonds and cubic zirconia.

The research yielded smooth castings and stones that were not clouded or cracked. Stone-in casting has been done for years, but not with platinum because the higher temperatures required to melt the metal damaged the stones.

Five Months of Testing

Robinson’s quest to perfect stone-in platinum casting involved working with six types of three-hour platinum investments made by dental supply companies. Over five months, Robinson tested two or three flasks a day, experimenting with different formulas.

He developed a formula that includes the proper mix of water and investment, as well as a process for exact control of time and heat during the casting process. He says the formula produces undamaged stones and smooth castings that appear almost as shiny as if they’d been tumbled right out of the breakout. The formula worked with all six of the quick platinum investments tested.

What it Means to You

This breakthrough is important for small manufacturers and bench jewelers. Casting a piece of jewelry with a gemstone set in the wax model is often much less expensive and time-consuming than setting it once the piece has been cast, says Robinson.

In another important development, Robinson discovered the casting formula allows platinum casting to be done in a room-temperature flask.

After completing the burnout, Robinson set the flask aside for more than an hour, allowing it to cool enough to pick it up bare-handed. He put it in the casting machine at room temperature.

When the casting was finished, Robinson broke apart the investment to reveal a smooth and shiny cast piece of jewelry. When hammered, the cast was malleable and did not break.

Lower-Cost Casting

The use of quick-setting investments with the formulas Robinson devised opens up the possibility of platinum casting to bench jewelers who, in the past, did not want to sink money into buying the equipment traditional platinum casting required.

Robinson stresses these developments will allow bench jewelers to cast platinum with far simpler and less-expensive equipment. He will send the formula to any bench jeweler who inquires.

The Precious Metals West/Fine Gold castings pictured here are the very first platinum stone-in castings where diamonds and cubic zirconia survived intact and undamaged. The feat was accomplished using a new formula for quick- setting investments.


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