Introduction

This activity shows you how to make a simple plaster sculpture using a clay mould. Students will make pebble-shaped sculptures that are decorated with simple relief motifs.

Pebble relief sculptures

The activity is inspired by a workshop led by sculptor Stephen Broadbent as part of Art UK's Masterpieces in Schools programme.

It is designed for KS 2 / CfE Level 2 students but could be adapted for older students by tasking them with creating more elaborate detailed moulds.

What is casting?

Casting is a technique that involves using a mould to make a sculpture.

Plaster or molten metal is poured into the mould – or clay is pressed into it – to form the sculpture.

Find out more about casting

Method

Step 1: plan a design

Task your students with planning and drawing a simple design.

This could be related to other subjects you are studying in the classroom – such as the seasons, the Vikings or Egypt. As the design will be incised into the clay it will need to be a simple motif or line drawing.

Step 2: make a mould

Give students a small slab or lump of clay each. This should be a little bigger than their pebble or stone.

Instruct students to push the pebble or stone into the clay and then remove it to form a hollow.

Using a clay tool or pencil, students can then draw their designs into the clay hollow.

Clay moulds with incised designs

Step 3: mix the plaster

As plaster can be messy with potential health and safety issues, this task should be undertaken by teachers. Make sure students are supervised at all times. Plaster dust can get into the eyes or nose so ensure that it is handled carefully and never mix or allow students to mix plaster with their hands.

The best ratio to use when mixing plaster is two parts water to one part plaster (you could use a paper cup to measure the quantities).

• Measure the water into your bowl.
• Gradually add plaster. Try to add it to different areas around the bowl so it doesn't build up in one place.
• Tap the side of the bowl occasionally to disperse the plaster and get rid of any air bubbles.
• You have added enough plaster when it stops disappearing into the water and sits on the surface (this is usually around the 2:1 ratio).
• Now gently stir the mixture to make it smooth using an old spoon or stick.

Top tip! If you would like to add some colour to the plaster, add acrylic or poster paint at the stirring stage.

Step 4: pour the plaster into the moulds

Pour the mixed plaster into the moulds. If you are filling a few moulds at the same time, line the moulds up together.

Pouring plaster into the moulds

Leave the plaster to set. (You will notice that the plaster becomes warm as it sets.)

Caly moulds filled with plaster

Step 5: reveal the finished sculptures!

When the plaster is hard and cool to touch, it is set.

Your students can now carefully peel the clay from the plaster to reveal their pebble relief sculptures.

Finished sculpture with mould

Variations and differentiation

Use other hard objects to create different shaped hollows for your incised designs.

Older students could make more elaborate moulds from clay by incising or carving a more detailed design into their clay hollows.

You could also press shaped objects – such as plastic or rubber toys – into clay and fill these indents with plaster to form shaped sculptures.

Silicone moulds

Silicone is frequently used to make high-quality, detailed casts of objects. It is a safe material for students to use but is more expensive than clay.

Use these links to find out more:

Tate resource: How to cast like Rachel Whiteread

Sea Museum: How to make cheap, easy moulds and casts