We ran out of sidewalk chalk the other day. Since it's still fairly warm here and the kids still play outside frequently, this gave me an excuse to make homemade chalk...something I've wanted to do for a long time.
Plaster of Paris, water, paint and styrofoam cups.
Pour 1/2 c. of plaster into the cup. Slowly pour 1/4 c. of water on top.
Let the water settle into the plaster a bit by poking holes in the powder before you start mixing. Make sure to scrape the bottom of the cup well to mix in all the powder.
Once it's mixed to a smooth consistency...
...add some paint. Remember the more paint you add the darker the chalk will be but it will also take longer for the plaster to harden.
Mix the color thoroughly all the way to the bottom.
It will probably start getting chunky now.
Tap the cup on the table to settle all the plaster and level off the top surface.
Leave the chalk to harden about 30-40 minutes, more if you added lots of paint.
If it feels hot to the touch then it's almost ready.
Tear or cut off the styrofoam cup for your chalk.
It works really well. It doesn't wear down as quickly as store bought chalk either.
I've read other ways of making chalk by using a mold of a toilet paper tube lined with wax paper. I haven't tried that but styrofoam cups seem simpler and they aren't too big for little hands.