Casting with black diamond, lost shine


I recently sent out a small object to be cast in brass with a rough unfinished black diamond. The cast turned to fine except for the diamond. Its covered in a white residue and has lost its black shine. Any suggestions on what the residue may be (from investment?) and how to polish the diamond back to its shine?


I don’t cast stones in place, always set afterwards so I can polish underneath. But in an attempt to help I’d say that the only reason a diamonds polished surface will actually dull is when it’s burned. Usually that’s when it’s superheated with a torch. The remedy is to have the stone repolished, which you cannot do if it’s a rough crystal. Hopefully it is just investment and only needs a good cleaning. Good luck.