Hello All,   I am having a persistent difficulty when using a spherical plaster mold I made. I have only ever had this issue with two-piece spherical molds (one was 8 inches, and this one is ten inches in diameter).    I pour the slip in, let it set for a thick wall (about an hour), then pour it out and let it dry in the mold (as usual). The problem is that, again and again, when I release the mold, I find that one half of the sphere has collapsed/separated from the plaster w