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SCIENCE

Making powder paints

Curriculum links

English National Curriculum:
Science Sc1: 2d, 2f & 3b

Approximate time required: 60 - 90 minutes

Resources needed

Per group:

Making powder paints sheet
Chalk (powdered)
Sample of blue pigment, in a transparent container from Supplier (see List of Suppliers)
Blue powder paint
Paintbrush
Yogurt pots or mixing palettes
Pipette
Teaspoon
Hand lens (optional)

Suggested organisation

Initial class discussion, followed by children working in groups of 2-4.

Carrying out the activity

The class look at samples of school blue powder paint and the blue pigment, and they are asked if they can spot any differences between them. The main difference should be the shade of blue - the pigment being much darker. Explain to the children that school paints are a mixture of powdered chalk and coloured pigment. Tell them that the chalk is added as it is a cheaper ingredient than the pigment and thus makes the paint cheaper to buy.

The children are now asked to plan an investigation into the effects of mixing different amounts of pigment and chalk. The teacher should suggest that a good starting point would be mixing equal proportions of both, e.g. a teaspoon of blue pigment and a teaspoon of chalk.

They can test their mixtures by adding an appropriate amount of water (which they may also choose to record) and painting a strip of the resulting 'paint' into a chart. Children can be given a prepared chart, such as the one provided on the activity sheet Making powder paints. More able children can be asked to create their own chart.

Children should discuss the criteria for choosing 'the best' powder paint mixture. These could include texture, appearance and cost. If children choose cost as a criterion, see the extension activity below.

Children can be encouraged to include two additional 'recipes'; one containing pigment only and one containing chalk only. In this way, children can compare the mixtures with the individual components. They should also appreciate that the chalk does not dissolve in the water, as the chalk remains on the surface of the paper after the water has dried/evaporated.

Extension / links

Maths
Children can extend the activity by considering the cost of the two main ingredients. They are given the following information (correct at the time of writing):

1 kg chalk costs £0.10    1 kg of pigment costs £3.00

The children can be asked to convert this information into the approximate cost per teaspoon before costing each recipe. This offers them a mathematical problem to solve. An example of a solution is:

4 teaspoons of pigment weighs 1g. Therefore, 4000 teaspoons of pigment weighs 1 kg.

Therefore, 1 teaspoon of pigment costs £3.00 ÷ 4000.

A similar calculation can be carried out for the cost of the chalk.

Alternatively, the approximate cost per teaspoon can be given to the children.

Science
Alternative grinding methods are investigated in the Grinding Chalk activity.

Design & Technology
After examining and discussing existing pots or containers for powder paint, the children could be asked to design packaging for their product, to try and produce bright, practical and eye-catching alternatives.