You will need:
plaster of paris
food coloring or tempera paint (we tried both…you choose)
1. Choose a mold. I think toilet paper tubes are too big. We use the skinny tube from the aluminum foil. Perfect size.
2. Better than the tubes themselves is an aluminum-wrapped version. I find that the pure tubes absorb too much water and keep the chalk wet for too long. Fold the foil underneath until it overlaps. Otherwise it will leak.
4a. Add food coloring.
4b. Or food coloring…
5. Fill the molds. Just blob it in like muffin batter.
6. We also tried egg cartons. Don’t do that. Scraped knuckles. Especially…the paper kind. Never dries.
7. Let dry over night.
8. Use in a day or two.
Review: We found that the food coloring changed the pigment of the plaster WAY faster. A WHOLE canister of pre-mixed tempera was needed for a cup of plaster and water. Only 10-20 drops of food coloring was necessary (except blue below…food coloring left, tempera middle, *real* store-bought chalk on right—–food coloring a bit light.)
However, while food coloring was more economical and dried faster, the chalk was REALLY hard. You need a really smooth surface. It’s like trying to draw with pottery.
$$: Plaster of Paris is about $4 for 4 lbs. Sidewalk chalk is about $0.87 for 4 ounces. For white chalk, Plaster of Paris is $.25 per pack (of store bought chalk). If you are going for economy, it’s all about your coloring choice. Hard food coloring chalk? Totally cheaper. Better colored, softer, tempera chalk? Maybe not cheaper. You decide.