Since *unlike the RTV mold which is self-supporting” you have to support a latex mold. That means that I had to form a box around the master and latex mold while it was still on the tile. Plaster poured around it will support the mold when you are making a casting.
Everything worked great – until I tried to get the casting out. I couldn’t. The problem was that everything fit so tight it created a vacuum between the negative and the outside of the latex mold. I ended up having to break the negative. It wasn’t a major problem as I held it back together for the second casting like a giant jig-saw puzzle. The solution would probably be simply to cut the negative in half – or – probably a simply groove cut into the negative would have allowed air to get behind the latex mold. I remembered afterwards that people who cast plaster allow a passage to let them used compressed air between the casting and mold.