Castor oil is an excellent release agent for natural latex molds that are made for pouring cement. Castor Oil also has a rejuvenating effect upon natural latex and will usually bring it back to its natural consistency after it has been repeatedly used.
Castor Oil is also a release agent between a natural latex mold and a plaster back-up shell.
Make a 10% solution by dissolving one pound of castor oil in nine pounds (approximatly one gallon) of alcohol. Brush or spray into mold. For a release between the rubber mold and plaster back-up shell, simply wipe it on the back of the rubber mold while on the model. After the rubber is vulcanized, let the alcohol evaporate and then construct your plaster back-up shell.