Third graders studied the art principle of contrast (and the structure of the spider webs we tend to have a lot of this time of year) and created their own webs by scratching through a layer of black tempura paint with a small nail to reveal a layer of oil pastel beneath. After discussing how contrast is used by artists (and having the students share a lot of personal spider stories!) the artists thickly laid down light colored oil pastels in a design of their choosing and then brushed on the black tempura layer. In a second class period, they etched their drawings with the nails. The effect is pretty cool, and the kids seems to love all aspects of the lesson - from viewing the spider web images to laying down the oil pastel and tempura to seeing how the color is revealed by etching.