I agree with JR97. Common shadey practice is to underexpose & overdevelop, or overexpose & underdevelop. But if you have the densities, and you can see the holes in the pennies that you want to see, then let your vendor work out the technique.
Yes. Pre-heat, cooling rate, thermal-shock, number of dip-coats, kaowool, all carefully controlled. Why using flasks? Casting weight? Highly-automated?
"Due to the superheat and reactivity of my copper casts, it has become a real pain to cast the copper parts."
How? Why?
Good question. All answers on point. Carbides, intermetallics. It does get a little fuzzy. Also, bonds in ceramics (primarily ionic but also to a significant extent covalent).
Regardless of the nature of the bond, I would try to avoid speaking of molecules whenever possible unless you are...