A publication of the Archaeological Institute of America
As Scott Whittaker, SEM lab manager, positions the skull under a microscope, Walsh watches the image of it on a monitor. (James Di Loreto/Courtesy Smithsonian Institution)
In November 2007, Bill Homann, Anna Mitchell-Hedges's widower, brought the artifact to my office in the Smithsonian's Museum of Natural History for examination. Slightly smaller than life size, it recalled a crystal skull in the British Museum, and it seemed to me to be a close copy of that object, at least in size and shape. However, it differed from the British Museum example in its more elaborate carving, extremely high polish, and separate mandible.
The similarity of the two skulls' size and shape can be verified using measurements and photographs taken at the British Museum in 1936, when the museum's skull was compared to the Mitchell-Hedges one, which was then called the Burney skull after its owner, London art dealer Sydney Burney. According to an article published in the journal Man, the British Museum (BM) skull is 17.7 cm front to back (glabellar-occipital length), and the Mitchell-Hedges (MH) skull is 17.4; the BM skull is 13.5 cm from side to side (maximum calvarial breadth) and the MH skull is 14. Many of the other measurements taken are equally close, but as the article's author, British Museum physical anthropologist Geoffrey M. Morant, notes (pp. 105-106), "A more interesting comparison can be made by superposing the outlines," which clearly illustrates how nearly identical the skulls are in size and shape.
Adrian Digby, a young British Museum archaeologist, commented on the measurements and observations made by Morant in a short article accompanying the latter's comparative study. Digby (1936: p. 108) offered the possibility that the
Museum skull was copied from an original skull, and that at a later date the Burney skull was a sort of composite copy relying for its proportions on the skull now in the Museum and for its anatomical detail on some human skull in the possession of the carver.
He came to the conclusion that it would be quite strange that
anybody wishing to carve a skull out of rock crystal, and taking a real skull as his model should modify its dimensions to fit those of another crystal skull which he would see was but a poor copy of nature. It shows a perverted ingenuity such as one would expect to find in a forger, but Mr. Burney's skull bears no traces of recent (metal age) workmanship; so this suggestion may almost certainly be dismissed.
Digby's analysis was perceptive. By copying the British Museum skull, then thought to be authentic, a forger would make his work look more legitimate. Unfortunately the science of the day was limited. Without modern equipment Digby was unable to detect any evidence of the skull's recent manufacture.
After my first encounter with the skull in 2007, Homann returned with it to the museum in 2008 so it could be filmed for a Smithsonian Networks documentary, "Legend of the Crystal Skull." Following up on my initial study, which included examining the skull under a high-powered light microscope, under ultraviolet light, and computerized tomography (CT scan) to determine what we could without harming the object in any way, I took two sets of silicone molds of surface tool marks for SEM analysis.
If the skull were actually Maya from Lubaantun, which was abandoned around A.D. 800, the tools used to carve it would have been sharpened stone implements combined with abrasive sand. Pre-Columbian lapidary technology has been studied with considerable detail for more than a century. Through my own research, I have compiled a large bibliography on stone carvings from controlled archaeological excavations in Mexico and Central America documenting the fact that pre-contact artisans carved stone by abrading the surface with stone tools, as well as wood, and in later pre-Columbian times, copper tools, in combination with a variety of abrasive sands or pulverized stone. No historic or ethnographic source of which I am aware indicates pre-Columbian lapidaries used hard metal, such as iron or steel, as filing, drilling, or cutting tools, or that they employed any type of wheeled or rotary technology (Walsh 2008: pp. 18-19).
Comparison of SEM (scanning electron microscopy) images of ancient and modern carvings shows the difference. A line incised with pre-Columbian tools appears as rough with a slight twisting, indicating the movement of the hand pushing a sharpened stone. Modern diamond-coated, high-speed rotary cutting tools show lines that are perfectly straight. Parallel lines within the incisions are evidence of permanently embedded abrasive. The sharpness of the cut and the exactness of the abrasive lines indicate the use of a hard metal tool with a very hard abrasive, i.e. diamond.
Micrographs of silicone molds from the Mitchell-Hedges skull reveal marks of high-speed carving tools and deeply cut parallel ridges left by permanently embedded diamond abrasive throughout the skull's carved components. Some of the marks indicate the use of cutting tools less than a millimeter thick, which means they would have to be made of iron or steel, and the impressions of wheeled tools visible in the carved elements of one of the teeth are less than a millimeter in diameter. Under higher magnification, polished areas show parallel lines with a skipping pattern, indicating the use of a high-speed tool.
It seems reasonable to conclude from the SEM images that the Mitchell-Hedges skull was carved in modern times with high-speed, diamond-coated rotary burring and cutting tools of minute dimension. The teeth alone show the use of a rotary cutting tool less than 2 millimeters in diameter. I believe that the technology under discussion is decidedly 20th century. Considering the skull's initial appearance in the 1930s, I believe it was created at about that time. The British Museum skull, from which I believe this is copied, was on exhibit fairly continuously from 1898.