First, you should prepare moulds for making chalks from Plaster of Paris. You need to use masking tape along with toilet paper tubes which are empty. Now cover one end or side of the tube by applying masking tape. Make sure you apply several layers to cover each end of the tube properly.
Next, take a large mixing bowl for creating the chalk mixture. Add cold water with Plaster of Paris and put in the mixing bowl. Make sure that the amount of Plaster of Paris should be double the volume of water. Then stir the mixture thoroughly to get it nice and smooth.
If you want to prepare many chalks at the same time, then you need to use more than one mixing bowl for preparing enough mixture. If you want to make the chalks more beautiful, you can add your desired colours to this mixture of Plaster of Paris and cold water.
After adding colours to the mixture, you should stir it thoroughly with a spoon and also keep adding more colours until you observe that the shade of mixture starts to change.
Now place the moulds on a flat surface and start pouring in the mixture of Plaster of Paris and cold water with the help of a funnel.
After filling up the moulds with the mixture, you should leave it for almost 24 hours. The chalk mixture will become hard during this period and you will have your multi-coloured chalks.