When the presence of Fe and Ni are too excessive to allow proper alloying into Gold you need to make a Copper addition to the melt to assist in acheiving homogeneity. The amount will very depending on the level of these elements, but typically somewhere in the range of 1/2 the weight of the problematic bar to as much as 5X the weight of the bar (in the case heavier Fe & Ni). The problem will also occur when you have other rare metal contaminants like Ta, Mo, Cr, Co where you may find an even larger Copper addition might be necessary. Good Luck.If you have a poorly mixed melt of karat scrap, how much variation can one realistically see between the top of the bar and the bottom of the bar? Say 1 cm thick.
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