If you want to make resin moulds, you will first need to make a mother plaster mould. This will be the main mould and by making it out of plaster, you make a stronger mould, one that will last for a long time. However, to make the mother plaster mould you will have to use the original sculpted object, which can be made from clay, wood, metal or any material. You will need to coat it with either a mould releasing agent, vaseline, or paint it with an acrylic silicone finish, so that the plaster will not stick to it. Even so, you have to be careful when removing the object or risk breaking it.
Place the object you want to make a mould of on a piece of plywood. If it is an intricate object then you will want to make two mould halves, so you will need to block off the sides you want to cast with small thin plastic, tin or plywood sheets.
Prepare the sculpture by coating it with vaseline, a plaster release agent, or with a clear coat acrylic paint spray. This will allow you to pull the plaster cast off easier.
Sift plaster of Paris slowly into a bowl full of water. Allow the plaster to absorb the water and mix to a creamy consistency, like a thick milkshake. Vibrate and shake the plaster container a minute or two to eliminate air bubbles.
Take a brush and coat the plaster on the sculpture or the part of the sculpture you are making the plaster mould of and allow to dry for a couple of hours.
Mix another batch of plaster and apply another thick coat of plaster to the sculpture. This coat needs to be applied thickly and does not have to be placed on evenly. Keep building up the plaster until it is about 2 inches thick. Allow the plaster mould to dry for a day.
Remove the mould blocks made of tin, plywood or plastic. If you made a cast of the entire object, then lift it from the plywood base. Remove the sculptured object. If you used a release agent you will notice that the plaster does not stick too badly to the clay. If you didn't coat it well enough, then you may end up breaking the sculpted object.