I’ve been getting my designs cast for about fifteen years with one
casting company. My designs require an “antique” finish, and I use
selenium toner to blacken the castings before they are tumbled.
Periodically, for months at a time, the castings will not blacken. I
tried liver of sulpher, but that was no better. The only solution I
have found is to anneal each piece. But simple annealing doesn’t
always work, in which case I have found that heating with a coat of
Cupronil will work. This adds a time-consuming step to my production,
and is a source of great frustration. The company that does the
castings says that nothing has changed in their process. Can anyone
offer any suggestions?