This section is included in some refineries and is employed for the preparation of gold alloy and the stamping of blanks for some gold coins such Krugerrands. Clean metallurgical conditions and the field induced in the melt make the induction furnace an excellent medium for alloying purposes. For example, at present, 22 karat gold is made from electrolytically refined gold and cathode copper. A 22 karat gold must contain a nominal 91.67% gold with the internationally accepted specification set at between 91.46 and 91.86%. In this way, the refinery has to set itself the much more stringent limits of 91.63 and 91.67%.
Electrolytic gold is melted first in the crucible and the copper added afterwards in order to minimize oxidation. The alloy is poured into vertical closed moulds to produce billets 12 mm thick for rolling. The billets are rolled to the required thickness, which being reduced initially by 1.5 mm per pass through the rolls. When the billet is almost to size it is passed through the rolls several times at the same setting to produce a more uniform billet. It is then punched to produce coin blanks which are slightly overweight. These are then tumbled in a soap solution to remove sharp edges and to clean the surface. The blanks are next sorted by weight, and those still overweight are ground down to the correct weight by allowing then to roll diagonally across a fast moving endless belt of aluminum oxide paper. The finished blanks are weighed in batches of 500, each containing exactly one troy ounce of gold, or in 2000 coins for smaller coins.