2-3 tbsps. tempera paint (powdered or wet)

1 cup tepid water

1 1/2 cups plaster of Paris powder

Mix the paint and water in a disposable bowl (like a large plastic yogurt tub). Gradually mix in the plaster of Paris, stirring with a metal spoon or a disposable paint stirrer stick until all the lumps are dissolved. (It will now feel about like the yogurt that came out of the tub!)

If you are using a two-part mold, pour the mixture into both halves and tap them gently to release any air bubbles. Let the halves sit for two minutes, then immediately close them carefully together and tape them shut.

For a singleton mold, you could simply use a small paper cup. Or use a cardboard toilet tissue roll taped around one end to a piece of cardboard - or for narrower chalk, slice the tube lengthwise and tape it together in the width you'd like. (If you slide a sheet of waxed paper into the inside of the tube, you won't have to clean the cardboard off the outsides of the piece of chalk when it's set.) Or use a popsicle mold. Or maybe better yet, those fun-shapes ice cube molds made from silicone - easy to pop the finished product out.

Let the chalk mixture set in the molds for a minimum of 24 hours. The larger the mold, the longer it will take to dry (plus, of course, the weather has something to do with drying times).

An option:  Mix the water and plaster together thoroughly first, then just stir in the color/s a little bit to create wonderful swirly chalk!