those put under a heat lamp for a few hours

http://www.runtimedna.com/Art-Materials-Vol.2-Dry-Shaders.html

materials are entirely dedicated to natural dry medias: charcoal, colored crayons, graphite pen, pastel cray, soft pastel, red chalk, rubbing graphite or even pop-art styles

Humankind has not woven the web of life. We are but one thread within it.
Whatever we do to the web, we do to ourselves. All things are bound together.
All things connect......Chief Seattle, 1854