human
I've heard that some people use a special kind of sand to make sand paintings. What is it?
assistant
That’s right, I have heard about this. It’s called “gesso”. Gesso is a mixture of ground-up gypsum (calcium sulfate) and linseed oil. The ground-up gypsum makes the paint dry faster, so you can paint over it more easily. The linseed oil gives the paint a nice texture.