What is the name of the stuff you add to a crucible to keep alumium from sticking or being lumpy.?

is your question about making a good mold or about melting alu?

You can add flux (e.g. borax) to alu. You can also put flux into your crucible before first use, that will make the metal stick to it less. Though as I only ever had new jewelry size crucibles I only done it with small ones and I doubt it's practical for large ones, I don't think they require it.

And if you cast a "life-size" cannon you should know what you are doing, you should not require advice from yahoo answers about mold making. Though I would consider for something like that a sand mold. You would need a pattern for the cannon in order to make a sand mold for one. Unless you have already one it will be quite some work, depending on elaboration.

the aluminum shouldn't be lumpy, though you do have to skim the impurities off the molten metal and you have to to that in any case. Get #319 casting aluminum. Make sure it's hot enough before you cast. While it's in the process of melting it's lumpy at some stage...

Are you sure you have done that before?

The stuff you add is called flux. Use a mold wash on a ceramic in a sand mold and on the crucible to prevent sticking.

sperm