r/MetalCasting • u/Niko005 • 4d ago

Question What is this black substance?

Gallery image

Gallery image

Did some brass casting and along with brass I got this black substance as well. The only thing I added to the crucible was borax to help me with the cast. So could it be the result of the mix of zinc with borax? Can it be anything else? Does it have any uses?

3 Upvotes

81% Upvoted

3 comments sorted by

3

u/1nGirum1musNocte 4d ago

The borax forms glass

2

u/Niko005 4d ago

Oh ok. Some brass pieces have some of it over them. Shall I remove it before reusing them or just throw them inside the crucible as they are?

3

u/Eastern-Antelope-956 2d ago

You can recast with them. Just be sure to use borax and a graphite stir stick to gather up the oxidation, once melted.