We did an art activity from the book Great Artists: Hands-On Art for Children in the Styles of the Great Masters by Mary Ann Kohl. We studied about Giotto (1266-1337) and his method of making paint. Many of his paintings were made with egg tempera paint on panels of wood. To make egg paint we:
added each color to a muffin tin
mixed yellow egg yolk with 2 tsp. water (whip 'til frothy)
mix egg-water with chalk 'til smooth and runny
The paintings were similar to water color but of course more textured as some of the chalk was lumpy after it was crushed. The kids enjoyed the process as much as the product.