This is also known as Oobleck, Goo, and Ooze. This is an outside project! Or you will have little flakes of green cornstarch everywhere, you've been warned. Have a bowl of water or a hose handy for rinsing off glop when you are done playing.
Food Coloring (we always use green)
Depending on how much you want, we usually do about 1 - 2 cups of corn starch.
Then add just enough water to get it to stirring consistency, approx 3/4 - 1 1/4 cup.
Add a few drops of food coloring.
Glop is a non-newtonian liquid, so you can slowly sink your hand into it, but if you try to go in fast, glop acts like a solid (careful you don't hurt yourselves). Try breaking off chunks of it, or squeezing it tight in your fist. Kids have a lot of fun with this stuff.
Do NOT rinse anything off in your sink. Use your hose outside. You do not want Plaster of Paris in your pipes.
2 parts Plaster of Paris
1 part Water
Tempera Paint (works better) or Food Coloring
Pick the shape of chalk you want to make and find containers to let it set in. Paper cups work well.
Depending on how much you want, we usually mix up about 2 cups of Plaster of Paris and 1 cup of Water. Pour about 1/4 cup into each cup, add paint and stir until desired color is reached. Let set overnight. Tear paper cup and peel off of the chalk. Have fun!