Archaeologists have developed a new technique to analyze the elemental make-up of prehistoric rock artwork using “X-ray vision” that can better preserve these valuable sites.
X-ray Scanners That Uncover Secrets Hidden in Ancient Cave Art
Archaeologists from the Shumla Archaeological Research and Education Center have discovered a new technique for studying the chemical composition of the materials used to create prehistoric cave art that better preserves these sites.
Soon to present their research at the American Chemical Society (ACS) Spring 2019 National Meeting & Exposition, the researchers hope that their techniques can spread to other sites so that archaeologists will no longer need to damage delicate, millennia old cave murals through current sampling techniques.
"In this particular work, we used a technique called portable X-ray fluorescence spectroscopy (pXRF), in which a handheld instrument can be carried to a site and used right there, on the spot," says lead researcher Karen Steelman, Ph.D. "It gives you the elemental analysis of a specific material, and is the first step in figuring out how ancient artists used different materials to make their paintings."
Their research was carried out at the Rattlesnake Canyon Site, sitting along the Rio Grande in Texas, which has a wealth of pictographs dating from as early as 2,500 BCE. Using a 105-foot-wide mural at the site for testing purposes, they were able to use pXRF on 138 areas of the mural where the composition suggested the presence of overlapping layers of pigment.
Using the pXRF, they were able to detect multiple layers of pigments, as well as unseen layers of black pigment, made from manganese, under layers of red, made from iron oxide. Normally, to identify the composition of pigment layers, archaeologists have to sample the pigments directly, which requires damaging the pictograph.
Discovering Signs of Vandalism
Steelman, along with fellow Shumla researchers Victoria Roberts and Carolyn Boyd, Ph.D., also found evidence that the site might have been damaged by gunshots. To confirm their suspicions, and hopefully to document them, they used the pXRF scanner to take readings from the suspect areas to see if any trace elements remained that might indicate ammunition.
"Unfortunately, we often see suspected bullet impacts at rock art sites," said Steelman. "Most of this is older types of vandalism from the early 1900s, and we used the portable X-ray to determine what trace elements were present."
The discovered traces of lead, mercury, and selenium that was limited to the damaged areas, providing strong evidence of damage from bullet impacts. While disheartening, the documentation of such damage at archaeologically important sites greatly increases the willingness of state and federal agencies to grant funding to improve conservation measures.