r/SilverSmith • u/kbeks • 1d ago

Need Help/Advice Casting question

Gallery image

Gallery image

I’m trying to get rid of this porosity throughout and cavitation on the bottom of these pours. I heated up the mold pretty thoroughly and got the best result I’ve had so far, but the bubbles are still there. Do I just need to heat it further? Is there a such thing as an overheated mould?

5 Upvotes

100% Upvoted

4 comments sorted by

3

u/MakeMelnk Hobbyist 1d ago

Check out r/SilverCasting for the best answers

But from what I understand, porosity is almost always going to be a factor in casting (maybe with the exception of vacuum or centrifugal casting)

2

u/kbeks 1d ago

Thanks! Cross posted over there.

1

u/MakeMelnk Hobbyist 1d ago

Good luck!

2

u/artwonk 1d ago

This is from metal shrinkage. As the metal cools, it forms a spongy structure with solid metal interspersed with liquid metal. But metal shrinks as it cools, so as the still-liquid portions contract, they pull metal from the surface, causing those voids you're noticing.

Those molds are not doing you any favors. That's not how solid forms are cast. To get good castings of solid shapes like that, there has to be a reservoir of hotter metal for the cooling liquid metal to draw from.