I could have sworn I read in these forums how adding borax into your investment can make your it stronger. I can't find it now I'm wanting to make a 2-part mold using plaster. I have Ultra-Vest but the mold I need to make will be larger than my small burn-out kiln. I don't need to use plaster but I'd like the investment not to crack when I pour in the Zamak so here I am. Any 2-part mold makers have a history of success with Lowes/Home Depot stuff? Or maybe with Ultr-Vest when not fired?