The basic process for making a casting are very simple once you have mastered them.

Making the mold

The initial mold is made from a material called Alginate, which is derived from seaweed. Alginate comes in powder form, it can be pink or white and usually smells of mint. It is the same material that dentists use to take casts of teeth. The powder is mixed with water to the consistancy of thick cream.
The liquid is then applied to whatever you are casting, for hands and feet the alginate is normally held in a container and the hand or foot inserted into the container. For faces, torso's and other large body areas the alginate is poured over the area. The alginate will set in about 5 minutes, depending on the consistancy, and the temperature of the water used. The colder the water the longer the working time. As the alginate is runny to start with you will have to keep catching the drips and scooping back onto the main area.

Once the alginate has set, if you have cast hand or foot you can now removed the mold. For face and body molds you will need to build a back support to keep the mold from flopping out of shape once you have removed from the person. The support mold is made from plaster bandage, which is the same as the material that is used to set broken arms, the plaster bandage is applied over the alginate to form a mask effect. this will set in about 5 minutes. Once the plaster has set hard the whole mold can be removed. You now have a completed mold ready for the casting.

Making the cast.

The cast is made by lying the mold on its back, so that it forms a bowl effect. To fill the mold a very runny plaster mix is made and swilled round the mold to give all the alginate a coating. The excess plaster is poured out. Further mixes of plaster are made and swilled round the mold, each mix is made slightly thicker. As the process is repeated the plaster will build up inside the mold. a final thick mix of plaster is applied by hand, with the finished thickness being about 2-3cm. A layer of plaster bandage is then added to give extra strenght to the casting.

Once the plaster has dried, usually about 10 minutes, The the whole thing is turned over and the mold removed. first the plaster support can be peeled away. Then the alginate is removed. Once that has been done the casting needs to be left to dry out fully. This can take a couple of days. Once it has dried you will need to clean up the casting, removing any defects, filling in any holes caused by air bubbles.