Cory Holliday almost didn't see the stick figure painted on the sandstone. His first impression was that it was a clever fake. A cave specialist for the Tennessee chapter of The Nature Conservancy, Holliday was searching for caves in a remote part of Fentress County on the Cumberland Plateau (Tennessee, USA) when discovered the foot-long painting of a dancing stick figure. The left leg appeared misshapen, and the right hand resembled a claw.

The rock shelter painting came as a complete surprise. "I knew that Native American rock art had been found in the area, but I didn't realize this was so significant," Holliday said. "My first impression was that someone had drawn it with charcoal." In fact, the artist most likely lived during the Mississippian Period between 1000 and 1600 CE and used a paint based on a prehistoric recipe whose main ingredient was pulverized clay. That's according to Jan Simek, a University of Tennessee anthropology professor who specializes in cave archaeology.

Last spring, Simek, the acting UT chancellor, visited the rock shelter site. Using a scalpel, he chipped off a tiny sample of the pigment and brought it back to UT for a high-level chemical analysis. The tests revealed no modern paint trace elements such as lead or zinc. What's more, Simek discovered that the reason the pictograph looks so fresh is because it's protected by a veneer of calcium carbonate leaching out of the sandstone.