Learning to dry plaster moulds is arguably the simplest lesson in creating these useful tools. The process is fairly straightforward as long as the correct conditions are maintained. If done properly, it will yield a uniform mould that will form the medium of your choice.
Select a warm, dry location that is draft-free to dry your plaster mould.
Place plaster mould on a rack with plenty of room for air to flow around it.
Make sure your mould will not be exposed to temperatures of 48.9 degrees Celsius or higher to prevent the plaster from becoming powdery.
Place an electric fan on a low setting near the plaster mould, but be sure to rotate the mould every few hours so that a new portion is facing toward the fan after each rotation. This will expedite the drying time.
Allow the mould to dry for a minimum of 24 hours. Depending on the density of the plaster, this is sufficient time for it to dry thoroughly.
Hold the mould lightly against your cheek. If the mould is cool, it is not finished drying. If the mould is ambient, or the same temperature as the air in the drying room, it has dried completely and is ready for use.