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Nickel white gold alloys require careful attention in melting, pouring ingots, annealing and fabrication.
As a whole, nickel white gold alloys are more difficult to fabricate than yellow gold alloys. The following information may be helpful in the manufacture of nickel white wrought products.
The white gold master alloy and fine gold should be carefully weighed according to the desired karat. When loading the crucible, the white master alloy should be put in the bottom and the fine gold on top. Boric acid flux should be used when melting the white gold alloys. A neutral or reducing gas cover is very helpful during the melting process to protect the molten metal from oxidation. The precious metal should be mixed well when fully molten and the surface should be checked for unmelted alloy before pouring.
Many old timers melt and cast their white gold twice to be sure they have a good mix. The nickel white alloys contain a large amount of zinc and a small amount of smoke is usually noticed when pouring. If white fluffy flakes are floating in the air, the metal is much too hot. The molten metal should be poured in a vertical, pre-heated, lightly lubricated mold. Rectangular molds should be used for plate and sheet stock. Round rod molds should be used for making wire. A quick steady pouring technique should be used, slowing down at the end of the pour to prevent excessive shrinkage in the top of the ingot.
After casting the ingot should be removed from the mold and allowed to air cool – DON’T QUENCH! The cast ingot should be pickled in a 10 to 20% sulfuric acid solution, rinsed well and scrubbed well to remove any surface oxidation. A 40 to 50% reduction should be taken during the rolling process before annealing the ingot. TOO SMALL A REDUCTION WILL CAUSE CRACKING DURING THE ANNEAL. The ingot should be coated with flux before annealing to prevent heavy oxidation in open ovens. The ingot should be annealed at 1400 degrees F for 20 minutes. DON’T QUENCH AFTER ANNEALING – AIR COOL the ingot.
The ingot may be pickled in a 10 to 20% sulfuric acid solution, rinsed well and scrubbed to remove surface oxidation. The 40 to 50% reduction should be continued following annealing instructions until the desired size is obtained. With proper care, excellent results in nickel white gold fabrication can be obtained.
Good Luck!