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Lumps from casting

Hi my question is, everything from casting has lumps. Can’t see lumps after emery, but lumps show up after polishing. How can it be solved?

Thank you

Finish to a very high sand paper grit , like 2500 to 6000.
Then go straight to a light rouge.
There are other ways, but this is the easiest for me.

You don’t say what kind of lumps they are or how big they are. If they are flux, try a new crucible and using less flux in the future.

If they are metal, it’s likely that you aren’t mixing the alloy well enough. Or you might be using old or contaminated metal.

If they are investment, it could be any number of causes, ranging from old investment, incorrect proportions of investment and water, temperature of the water and/investment isn’t right or it could be that you are burning out too fast.

Without more info as to the nature of the lumps it’s hard to say anything more helpful.


Could be porosity presenting itself as it’s high polished. Try Hans’s technique. Could try burnishing first. Metal should polish nice though, so it could be polishing technique or metal irregularity.

Your castings should not have “lumps”. My best advice is to tweak your casting technique or hire a professional caster. If you are already using a pro caster, then it’s time to switch casting houses.
As for finishing imperfect surfaces follow the previous advice about finishing with super fine emery and very very lightly polishing it after. Over buffing and abrasive wheels tend to drag out surface imperfections.
Have fun and make lots of jewelry.
Jo Haemer