I'm a ceramic newbie and have been making two-part plaster molds and then casting solid plaster objects. Now, I'm experimenting with making two-part molds for slip casting with Liquache, a liquid paper mache product. The problems I've been experiencing suggest that something in the molding making process is affecting the absorption qualities of the plaster molds that I'm using in these slip cast-like Liquache projects. It occurs to me that the heat produced by curing plaster may well cause the oil-based clays to leech oil into the walls of the finished two-part plaster mold, thus impeding the passage of water out of the slip. So, I've been trying to find a clay that is suitable for use in making two-part molds, filling undercuts, etc., that is not oil-based. I know nothing about clays and there are so many different kinds on the suppliers' web sites that I can't tell what might work for me. Can anyone suggest the best non-oil clay that could be used in two-part mold making for slip casting?