Gold Mixing Calculator

In short Melting two lots of gold together gives a karat weighted by WEIGHT, not the average of the two karats — and that distinction is the whole tool. Ten grams of 24K melted with ten grams of 18K does give 21K, because the weights happen to be equal. Five grams of 24K with fifteen grams of 18K gives 19.5K, not the 21K a plain average suggests, an error of 1.5 karat that is worth real money on any serious quantity. The arithmetic is simply the total pure gold divided by the total weight, times 24. Two consequences follow and both matter. The first is that melting can never raise the result above the purer of the two inputs: alloying only ever moves the karat between them, and raising purity genuinely requires refining, which is a chemical process that also loses metal. Anyone offering to increase your karat by melting is describing something that cannot happen. The second is that the result may not be stampable at the karat it computes to. A hallmark is a guaranteed minimum, so 19.5K — 812.5 fineness — cannot carry a 21K/875 mark and would be stamped 18K/750, the highest standard it actually satisfies. Below 375 fineness the alloy cannot be hallmarked as gold at all in most markets.