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White Gold; During my thirty-three year search for the optimum precious metal alloys suitable for investment casting, white gold alloys have gone through quite an evolution of their own. My attempts to make an 18ct white gold have lead me through the nickel / palladium alloys and many combinations. Nickel containing white gold 18ct alloys gave me no end of problems. Although I made and cast a lot of this metal, my success rate was not as profitable as desired, so I concentrated on palladium as the whitening agent for white gold alloys. Casters found the nickel alloys easy to cast due to the lower melting/casting temperatures, that is in the 950-1050'C range for nickel alloys versus 1200'C+ for Pd alloys, but the ensuing cast quality of nickel gold alloys has not provided the most desirable consistency. Gold / nickel alloys although cheaper and whiter than the palladium alloys were more problematic both in casting and handling at the bench. Where, if not treated carefully at all stages of manufacture, castings would present problems to the jeweller and the setter, with claws and beads that would not bend without breaking, but worse, shanks breaking after sale.
I ultimately settled for a 12% palladium alloy which, while not producing a very white alloy, at least was cost efficient when marketed against the nickel alloys. This alloy's main attribute is in being a very stable alloy at all stages of manufacture. Furthermore, I found 12% Pd would give a colour that was acceptable. Albeit I was often told, to my chagrin, "Anyway it'll be plated, so who'll see it". With the use of Pd alloys, setting is much easier, the claws and beads stay on, and shanks do not break. After some time I was able to convince some customers to pay a little more to take a 15% Pd 18ct white gold which has a much better colour, although still toward grey rather than white. This 18ct Pd alloy is the one we still use largely, unless I can convince someone to take a Pd / Pt alloy. The addition of 5% Pt gives a superior white colour. Due to the higher melting point of these alloys and the mould temperatures required it is recommended that phosphate-bonded investment be used to achieve smooth castings. Rather than by means of electroplating, I consider that by means of alloying, the natural colours of the metals can be used to obtain the colours required. |
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