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Homemade Chalk

In this activity, students have the opportunity to make their own sidewalk chalk while learning about mixing pigment to obtain different colour combinations.

Objectives

  • Describe how different colours of light mix to give new colours.

Materials

  • plaster of Paris
    cold water
    large stir stick
    powdered tempera paint (red, blue, yellow) and scoop/spoon
    large pitcher

    Per student:

    3 Dixie cups
    3 Popsicle sticks

Key Questions

  • What happens to the colour of your chalk if you add more or less tempera paint? How do we get purple, green, or orange-coloured paint or chalk?

What To Do

Set up

  1. Just before starting the activity, make up a large batch of plaster in the pitcher by mixing one part water to two parts plaster of Paris. Stir thoroughly. If the students are older, they can make it themselves.

Activity

  1. Hand out the Dixie cups and Popsicle sticks.
  2. Students can put some of the powdered paint in each of their cups. They can put just one colour or combine a couple.
  3. Pour some of the mixture into each Dixie cup until it’s about half full and ensure the students mix the plaster with their powdered paint thoroughly.
  4. Let dry (should take about 20–30 minutes).
  5. Peel the chalk from the cup.

Teacher Tips: 

  • Plaster of Paris solidifies EXTREMELY quickly, so you’ll want to begin pouring as soon as you’ve finished mixing it!
  • Remind students to stir all the way to bottom of their cups and to remove popsicle sticks after they’re done stirring.
  • To simplify the clean-up, use plastic milk jugs (just cut open the tops) as pitchers for mixing/pouring the plaster. 

Extensions

  • Add more or less paint to get the colour you want. Is the dried version the same colour as the wet version?

Other Resources

Science World Resources | Full Unit | Colour and Light