Metal and Machinery

Not all alloys are suitable for stone-in-place casting. Successful casting this way requires a metal that will ensure as good a fill as possible. “The old belief was that if the metal wet the mold—if it contained more zinc and silicon—it would fill better and be better for casting,” Teague says, adding that the outlook isn’t necessarily true. “With the newer alloys, especially in white gold, it’s almost the opposite of what we used to believe.”

One alloy development that fits the bill is germanium white gold. “It increases the surface tension of the metal,” Teague explains. “That allows the metal to pass by the stones and the investment to get a better fill.” The only real downside to germanium alloys, he says, is that they cost slightly more. Naturally, good stone-in-place casting isn’t limited to white golds. Schuster notes that several companies are now creating more stone-in-place-compatible alloys in several karats of yellow and pink gold, as well as white. Schuster has also personally lead the development and refinement of this technique using 950 platinum, which he introduced in 1999, and in titanium, which he rolled out in late 2004.

Higher-end static vacuum-assist casting machines are also helping the process along. According to Teague, what’s most important to look for in these machines is their accuracy during the pour. “When you’re casting wax-set pieces, you want [as perfect as possible] an alignment between the pour hole in the crucible and the opening in the flask,” he says. “If you’re off-center, and you have metal bouncing down the sprue side-to-side because it’s off-center, then you have the possibility of non-fills just from turbulence.” As stone-in-place becomes more and more common, further advancements will certainly come along. After all, stone-in-place is about reducing time and labor and increasing productivity, and there isn’t a jeweler out there who isn’t interested in that.