I've done some searching around here but not really found the answers. I have run out of investment for jewelry casting I see here that some of you make your own This is interesting because the cost of shipping doubles the cost of the stuff. So I find that 50/50 sand plaster mix will work but I see also that some say 30 mesh silica sand ( Lowes has no idea what I'm talking about) and some say brick sand is fine. Is that the same as costurction sand or is it sand box sand?