Precious metal castings, like the Market Harmony silver and Valcambi gold pieces shown here, are part of a market worth $5.5 billion annually.
De-oxidized versions of the metal can alleviate this step. Gold also can be purchased in a de-oxidized state or with other additives that make casting it more economical and less prone to scrap production. 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 op- erations, 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 fi rst must be cleaned through abrasion or blasting in stainless steel shot, shined and burnished, and fi nally polished. Manufacturers might also use a chemical treatment process known as pickling. The pickling treatment, composed of a sulfuric acid type solu- tion, is particularly benefi cial on pure gold products, Arvay said, and can streamline 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 pro- cess,” 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 produce the original casting,” he said. According to the Valcambi spokes-
person, the company employs almost no fi nishing operations. “We don’t do fi nishing. It’s not nec-
essary,” 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.” METAL
Valcambi, one of the world’s largest producers of cast gold bars, produces the bullion in both the permanent mold and continuous casting processes in an automated facility.
26 Metal casting Design anD purchasing March/april 2010
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