Casting with plaster

Making a press mould of a tile

This short time-lapse video shows the making of a press mould for a clay tile. Keep your design relatively simple. We have made a design of a bird. It is important to avoid undercuts otherwise the clay will stick in the mould.

Follow the simple steps in the video and you should have success.

Making a press mould of a 3D object

This video shows the making of a press mould of a 3D object. The most important part of this process is finding the casting lines. If your object has undercuts the plaster mould will grip to the original. We have chosen a very simple example to demonstrate, a plastic duck. If your object is more complicated or not plastic, you will need to use a liquid soap release agent to help the original come away from the mould.
Watch the video a few times before you begin and maybe start with a relatively simple object.

Health and Safety with plaster

Plaster of Paris is available in most hobby or art shops and is not dangerous if used responsibly however a Risk Assessment is required. The two main risks with plaster are that it is a fine powder and that it generates heat when it sets. As with all fine powders they should not be inhaled and should be handled carefully to produce minimum dust. The heat produced by setting is only a risk if casting parts of the body. We would NOT recommend casting parts of the body. Plaster can occasionally irritate skin. To avoid this risk students and staff can wear gloves when handling plaster.

Using plaster in the classroom

Never pour wet plaster down the sink as it will set and block the sink. Always allow plaster to set in the mixing container and then crack out. We would recommend only mixing small amounts of plaster at any one time.

Avoid getting plaster into clay that is to be fired in a kiln. Even small amounts of plaster will make the clay explode in firing.

Protect clothing with aprons or overalls.

The work of Peter Palmer in Portsmouth Museum

In 1976 Peter was a student in Portsmouth and for his final show he produced a sculpture in stoneware clay made by casting his own body. We believe this work was press moulded using about thirty moulds and the finished fired sections were then joined together with resin. You will notice from the film the clay shrunk during firing making the sculpture smaller than the original. We would NOT recommend casting parts of the body because of the heat generated by plaster setting.