In the Spring of 1971, two medallions were found during the excavations being conducted at the San Diego Presidio under the sponsorship of the San Diego History Center and in cooperation with California State University, San Diego. The medallions were badly corroded and beyond identification by non-destructive means. Dr. Paul Ezell, director of the excavations, wanted the two medallions identified, which led to the idea of using x-ray. Dr. David Adams, a private radiologist in San Diego, became the radiology advisor on the research, and donated his time, equipment and film.
One of the problems facing the archaeologist today is finding a non-destructive means of examining and identifying artifacts. The proper identification is imperative in providing information about the culture the artifact represents. Often, however, it becomes necessary to destroy a part of the artifact in order to determine the identity of the artifact and of what materials it is made.
A means which is possibly of great value is that of radiology. X-rays have been used to identify objects of various materials practically since its inception. However, it has been done only in isolated cases and with specialized equipment. Through research, it is my contention that nearly all objects derived from an archeological site can be either identified by, or have light shed on by the medical x-ray machine.
At the present time there is readily available extensive x-ray equipment in any city in America, and in most hospitals throughout the world. In addition, it is common experience for a radiologist to have an unusual item brought to him to be radiographed. However, without any standard reference of exposures and techniques available, the radiologist must frequently experiment to obtain adequate x-rays, and then still those obtained may not be ideal.
With further research, I hope to make available a basic standard of techniques for making radiographs of diverse items from organic material to marble and heavy metals, and exactly what one can expect from these exposures. Therefore, the possible benefit of x-ray to anthropology would be available world wide.
To evaluate the possible value of radiographing archeological and anthropological objects, one should start at the beginning, in the soil before they are completely recovered. While it is not yet possible to accomplish this, it is conceivable that in the future the specimen may be radiographed before it is removed. This may be accomplished by an x-ray probe which extends beneath the item and radiographed upward. Or it may be accomplished by tangential x-rays or scatter x-rays off the object itself.
It is readily possible at this time, however, to radiograph through soil, or adobe or foreign material to locate items deep within the soil. Metal in particular, can be readily identified and radiographed in the laboratory in a box filled with soil of various depths.
A great deal of the past year has been spent working primarily with metals. Most of the artifacts used in regard to this research have been coins and buttons and medallions collected at the Presidio site. Their ages range up to as much as two hundred years old. It has been possible to determine on the external surface the outline, engraving, or painting on the metals. The outsides are usually deeply corroded and it is impossible to make out by the naked eye. The only other means of examining these artifacts are by chemical analysis, which is often destructive not only to the outside surface, but sometimes dissolves the artifact itself. With the present technique we can also show the internal structure of metallic objects showing fracture or fissure and the crystalline internal anatomy.
In addition to metals, work also has been done in radiographing rocks and shells. It is apparent that identification of small chips of either of these objects can be made through x-ray. Once magnified the internal structures of the rocks and shells are different from one another. The importance of these identifications have bearing when viewed in the light of cultural contact. If for instance, a wooden bowl with a shell inlay were to be found at the Presidio, and the shell was of conch not found in this area, but only found at Conception Bay, Mexico, it is relatively safe to assume there had been contact between the two cultures. This approach can be applied to other materials such as pottery, food, wood, etc.
The possibilities are as yet inadequately explored so far as to what radiography may someday offer the field of anthropology. However, through this research some things have definitely been established. As an example, x-rays can tell a great deal about the external surface of an artifact. In addition to determining the outline, engraving or painting on the coins previously mentioned, x-rays can identify a painting or carving which is faded and indistinct. Radiography can prove the presence of paint, coating or preservatives on an object. It makes it possible to identify bone which is fragmented or decalcified, or identify a leaf or basketry on another surface, or show a fragmented or irregular surface. These are all examples of what an x-ray can tell just about the outside surface of an object. However, radiology is unequalled for what it can tell us about the internal structure.
Most important, non-destructive detail of any structure from 1.11 mm. of organic density to several cms. of heavy metal can be shown. However, in addition, the amount of use, construction methods and repair can be proven. Often it can determine the age, sex, disease or matching pair of bones. One last important recommendation is that of the ability to verify authenticity which is imperative to the anthropologist.
This research is at the moment at midpoint, which includes some accomplishments and a great deal of possibilities. If progress is steady, when the project is completed, a “cook book” type manuscript will be made available for anthropologists and radiologists alike, giving a list of standardized techniques for all objects extracted from an archeological site. Hopefully, by resolving one problem for the archeologist, it will make the science more exact, and with less unavoidable guesswork.
Ellen Gooley Lennert is an archaeology student at California State University, San Diego. Her research in the uses of radiology in archaeology has been conducted under the aegis of Dr. Paul Ezell, professor of Archaeology, and Dr. David B. Adams, a San Diego radiologist.