Age group: Any
black ACRYLIC paint (not the tempera-the acrylic covers better and dries faster)
scratch tools like toothpicks or pop cycle sticks.
Start with a white piece of paper (I used regular computer paper), and have the students color hard and dark with crayons until the complete sheet is covered. The brighter colors: the better the results. I kept reminding the students not to leave any white spots.
This is the first step, half way finished.
After their 2nd grade arms were ready to fall off from coloring, we painted over the entire page with black tempura paint mixed with just a drop or two of dish soap. (The dish soap helps the paint to adhere to the waxy crayon).