I want to fabricate and cast crystals to then cast in glass. I've done glass casting before, but not much mold making. If I have a wax positive, I can melt it out of the plaster/silica mold so it doesn't have to be a 2-part mold as long as there aren't any undercuts, which there won't be. My question is how can I fabricate and then cast crystals to then cast in wax to make my glass mold? I'd like to work with silicone since it is flexible and then I won't have to make a 2-part mold. I thought about cutting foam to make the crystals, but I want the edges to be very smooth so that the glass casts look like crystals. I also thought about carving glycerine soap and casting that, but not sure how it would hold up to being cast with any flexible mold-making materials like silicone. Any advice?