Plaster is much like some air dried clays. It does not have to be baked and it is very solid when the work is completed. It can be painted, varnished and decorated the same as any other sculptured piece.
For small to medium size plaster sculptures you can use any plastic bowl, container or bucket that is the height you want the finished piece to be. The container must be flexible so you can remove the piece when it has set.
Plaster is best carved as soon as you have removed it from the mold or container. It can still be carved after it has dried, however, you will then have to use sandpaper and sharper tools. If you get the major parts of the sculpture done before it sets, the finer details can be added later.
You should have a perfect mental idea of what you want to carve or a picture of what you want to create as a reference while you work.
If you have never used plaster before you should start with something small and gradually increase to larger items after you have become familiar with the process of mixing plaster. All Plaster of Paris products have written instructions on the package. It's best to follow these instructions explicitly. The usual mix is one third water and two thirds plaster. The amount of water to use is determined by filling the flexible container with water and sprinkling in the plaster until all the water has been absorbed. Do not stir the mix until you are ready for it to set.
For larger items mix the plaster in the container you are using that is the size you desire. You can also create huge blocks of plaster and cement them together with additional wet plaster.
Smaller items can be mixed in paper or styrofoam cups, plastic margarine tubs or paper milk cartons. Begin carving as soon as the piece is removed from the container.
Large size or life size sculptures can also be created with plaster coated gauze rolls. It's the same thing doctors use for making casts. The strips can be purchased pre-made. All you do is soak them in water and smooth them in place. You should first make a form using chicken wire , which you can get from any home improvement store. Then add the strips the same as you would paper mache, building up the areas you need to.
Don't try to duplicate a body part using the gauze strips. Plaster gets very hot as it is setting and you could get serious burns.
Nicks and mistakes can be easily corrected by dabbing on a bit of wet plaster and smoothing it out. Recarve the section if needed.