The lengths some precious metals
casters will go to preserve their metal has become the stuff of legend. Not only do the producers collect the dust that gathers in the fi nishing room and fi lter the water used in fi nishing opera- tions, others have been reported to collect the gold dust that gathers on workers shoes.
Finishing the Product Precious metal bars have to look
good. Whether the purchaser is an investor looking to buy a product that will appreciate in value or a hobbyist looking to buy a piece to add to his or her collection, cosmetics matter. And for some casters, the only way to achieve that kind of fi nish is through post-processing. According to Arvay, precious
metal castings first must be cleaned through abrasion or blasting in stainless steel shot, shined and burnished, and fi nally polished. Manufacturers might also use a chemical treat- ment process known as pickling. The pickling treatment, composed of a sulfuric acid type solution, is particularly benefi cial on pure gold products, Arvay said, and can stream- line the fi nishing process. It’s best used in large volume operations, but it is not without its costs. “It removes the heat staining
and patina, and you can stop after the process,” he said. “But there is a disposal cost of the acid and safety issues.” While Arvay’s company employs extensive fi nishing operations to bring his castings to the cosmetic level his customers require, he’s realistic about his capabilities. “The fi nishing process you use is dependent on how well you pro- duce the original casting,” he said. According to the Valcambi spokesperson, the company employs almost no fi nishing operations. “We don’t do fi nishing. It’s not necessary,” he said. “The way we pour it, the bar is clean and ready to stamp and send out. They require no polishing afterwards and no brushing.”
MC Online Resource
Visit
www.goldprice.org/ for current pricing for both gold and silver.
MODERN CASTING / September 2010 21
With the high cost of gold, casters are careful to maximize the alloys used in their processes. Metal loss is unacceptable in the world of precious metal bar production.
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