Black Bronze dust can be made in the crafting table using gold, silver and copper, and can be centrifuged back into those elements. However, the mixer recipe uses 2 gold dusts instead of 1 gold and 1 silver, which I don't think is intended (it also effectively allows for turning gold into silver).

The mixer recipe currectly uses 3copper+2electrum, which is the same as 3 copper+silver+gold.