Engineering Techniques Help Answer Questions On Ancient Egyptian Artwork

The researchers used a scanning electron microscope (SEM) capable of working at magnifications over 100,000 times for microstructural and microchemical study.

"The success of the research was due to the availability of CWRU's state-of-the-art laboratories with characterization facilities," said Arthur Heuer, the Kyocera Professor of Ceramics in CWRU's Department of Materials Science and Engineering.

"The collaboration between materials scientists and conservators at the Cleveland Museum of Art was key and shows how a nondestructive surface technique can be used to investigate ancient technology and the composition of ancient artifacts," he added.

The glazed faience objects represent more than 2,000 years of production. The fired ceramic bodies typically contain more than 90 percent ground silica (quartz, flint, or sand) and small amounts of soda-lime-(calcium)silicate glass necessary for vitrification or hardening. (Ordinary window glass also is a sodium-lime silicate composite). The surfaces are typically continuous copper-blue soda-lime-silicate.

"There were several unanswered questions about this collection of objects from a materials standpoint, necessitating better characterization of the technology," said Pat Griffin, assistant conservator of objects at the art museum, who has worked on the project since 1997. Griffin worked primarily with John Sears, at CWRU's Center for Surface Analysis of Materials as part of CMA's ongoing research into its Egyptian art.

"There are visible differences between many of the faience objects related to paste formulations and various manufacturing processes, including glazing methodology, paste additives, and the degree of vitrification or hardening during firing," Griffin added.

Examination using the scanning electron microscope -- in conjunction with replication experiments Griffin conducted -- enabled researchers to understand the effects of grain size on the objects' composition. Although most faience ceramics are chemically similar, the fineness of the particles has a dramatic effect on the way the damp faience paste is worked and on the final appearance of the fired and glazed product. Research shows that variations in the glass content and lime content also had visible effects on the working properties and final appearance.

The CWRU researchers, under Heuer's direction, also provided valuable expertise in the study of six small gold and silver beads from the Middle Kingdom. This period, around 2000 B.C., was early in Egyptian gold working. For the gold and silver objects, Griffin noted, "interest is focused on understanding the sophisticated construction and soldering techniques used in their fabrication." The CWRU/CMA team found that the gold and silver objects were made using a combination of colloidal hard soldering -- often referred to as granulation -- and hard soldering using a lower-melting-point alloy introduced into the joint.

This collaborative research between CWRU and CMA aided Griffin in studying the materials, construction, and condition of these objects, as recently published in the Catalogue of Egyptian Art (Lawrence M. Berman with Kenneth J. Bohac, Cleveland Museum of Art, 1999). Some of these objects are on display in the CMA's Egyptian art gallery.