Thursday, October 28, 2010


Back in the early 1980s, I first heard of a very exciting analytical technique being applied to art history studies – neutron activation analysis. This was described in an article by Maurice J. Cotter, Neutron Activation Analysis of Paintings published in the January-February 1981 issue of American Scientist magazine (pages 17-27). It is based upon the same general phenomenon as C14 dating, that each element has its own discrete atomic half life. If you can use some form of radiation source to irradiate a sample and induce radiation in it, the rate with which that radiation dissipates (its half life) can be measured and analyzed to identify the discrete elements in the sample and their respective proportions. Of course, that reading would be of the remaining elements of the paint as well as the elements in the surface that the paint is on. By taking readings of an adjacent area of unpainted stone surface, a comparison would then illuminate the contents of the paint. Simply put, any difference in the readings between the two areas can be assumed to represent the contents of the paint. At the time I recognized that having portable equipment to do this would allow us to begin to identify the pigments used in the paint of pictographs, but alas, I am not a nuclear scientist.

Multiple colors, Notches Dome, WY,
Photo-Bonnie Newman, 2005

A technique similar to this has now been applied pigment analysis of rock art in just that manner in a fascinating project conducted by Bonita Newman and Dr. Lawrence Loendorf. They used portable x-ray equipment in July 2005 to analyze the elements in the pigments of pictographs at rock art sites. Newman described the process as follows:
Dr. Loendorf  taking a reading, Photo - Bonnie Newman, 2005

“Pigment analysis at the three selected sites was conducted with a portable x-ray fluorescence spectrometer. This small, light hand held unit provides non-destructive elemental analysis.

As the atoms of an element are struck by high energy photons from the x-ray source, electrons from the inner shells are knocked from their orbits around the nuclei of the atoms, causing those atoms to become unstable ions. To re-establish stability, electrons from the next higher shell move to the vacant inner orbits emitting energy as they move.

This phenomenon is referred to as fluorescence. Since each element maintains a different electron shell configuration, the spectrum produced by each episode of fluorescence is unique, allowing the element to be identified.”

Now think about how important this actually is. After a century of guessing and making assumptions about the chemical contents of the paint used in producing pictographs we can now know exactly what those elements are! Think of what a database this will eventually be.

In a future posting I will discuss some of the results of their studies.
Bonita Newman is an archaeologist with ICI Corporation, Virginia Beach, VA., and is currently a member of the board of directors of the Colorado Rock Art Association. Lawrence Loendorf is a noted rock art researcher, a former president of the American Rock Art Research Association, and is a retired New Mexico State University professor.

No comments:

Post a Comment