It was a beautiful day in sunny California . Marc "Doc" Robinson of ABI Precious Metals in Carson was at home tuned into one of the shopping networks when a segment on platinum-plated silver jewelry started. Eyes glued to the tube, the alloy mixologist had a revelation. He began screaming at the television, "Put the platinum in the silver!" He yelled this phrase over and over, louder and louder with each repetition, until eventually his wife Inday ran into the room to make sure everything was okay. Not only was everything okay, Robinson thought, but the day just got a little more beautiful: a new alloy was born.
From that day, it took about two months of experimentation to get the formulas for Platinum Sterling Silver just right-Robinson created alloys containing 5 percent, 3.5 percent, and 1 percent platinum. But he's the first to admit that combining silver and platinum isn't a novel concept.
"Some large manufacturers use between 75 and 90 percent silver, 5 percent platinum, and 5 percent other metals," he says. "What's different about this alloy is that it's 925 sterling silver and platinum, so it doesn't tarnish like traditional sterling does."
|Platinum Sterling Ring, photo by Gary Dawson.
When asked what's in the new alloy, Robinson gives up the following ingredients: copper, zinc, a few dashes of mystery metal, and a hardener (also a mystery). The formula results in a bright white metal that, when held up to the sunlight, flashes a rainbow of colors, from purples to pinks to greens.
So what's it like to work with this stuff? AJM asked Charles Bennett of Roberto Martinez Manufacturing in San Clemente , California , who's been working with the alloy on his own and overseeing numerous tests of its workability. "It's one of the most enjoyable metals I've worked with," says Bennett. "It acts like a 14k yellow during fabrication and setting, but it's stronger. It has the ability to be rolled, stretched, and drawn far beyond the limits of conventional sterling silver or karat gold."
Bennett, who oversees manufacturing for Roberto Martinez, recently conducted drawing tests in the company's Bangkok facility. The experiments were successful, and the company debuted a line of hoop earrings and bracelets at JCK Las Vegas in June.
In an in-house testing procedure, Robinson rolled a 1/2 inch-thick bar down to 2 mm without annealing. "It rolls like butter," he reports, adding that the metal can be age-hardened to 80-85R-15T (Rockwell hardness). When rolling, the metal reaches 90R-15T. It can also be heat-treated; Robinson suggests annealing at 1,050°F (565°C) in an oven for 30 minutes and quenching to achieve 70R-15T.
In addition to Roberto Martinez, other manufacturers have conducted tests on the alloy. As a result, the 1 percent formula has been manufactured into chain, and the 3.5 percent has proven successful in stone-in-place casting with rubies.
When it comes to casting, Platinum Sterling provides one main challenge: with the addition of platinum, the metal freezes much faster than traditional sterling, so you need to use higher flask temperatures. For example, Robinson explains, a typical flask for casting sterling silver should be between 750°F and 1,000°F (399°C and 538°C). For Platinum Sterling, Robinson recommends elevating the flask temperature to between 950°F and 1,150°F (510°C and 621°C), depending on the piece.
Despite the higher flask temperature required, typical casting equipment for gold and silver is suitable for use with this alloy. Robinson notes that casting tests are ongoing, with data such as phase diagrams and cooling curves to come.
Another area in which research is ongoing is solder. Robinson says that it has been difficult to find a low-temperature solder that matches the brightness of the metal. Currently, three formulas are in the final testing phases, and Robinson is confident that one will be a perfect match. In the meantime, he recommends using 10k white gold plumb solder for repairs.As Robinson continues to fine-tune solder formulas and conduct additional tests on the alloy, he is optimistic about its market potential. "People love sterling silver," he says. "By elevating its perceived value, we boost the price point and create a whole new market."