Thermochromism. A hand print on thermochromic paper. The paper has a liquid crystal compound encapsulated to its surface. The spacing between layers of the crystal is sensitive to heat - as heat is applied the distance between layers decreases. At room temperature, the distance is such that the crystal absorbs light (appearing black). As it heats, the distance decreases and the crystal reflects a specific colour depending on the heat from reddish-brown (coolest) to blue (warmest). The crystal will eventually return to room temperature and the hand print will disappear.