With National Science Foundation support, Dr. Chandra Reedy and an interdisciplinary team of students at the University of Delaware will develop and test new procedures for using inexpensive light microscopes to better understand ceramics, one of the most archaeologically-significant classes of materials. They will modernize the technique of thin-section petrography, which uses small samples mounted on a glass slide and ground down to 30 microns thick. When examined under a microscope with polarized light, minerals in such samples are identifiable by optical properties. Thin-section petrography is used to characterize archaeological ceramics and investigate ceramic production, function, exchange, technological style, and use history. However, the technique is often marginalized because of some challenges. For example, traditional methods of obtaining quantitative data from thin sections are very time consuming, but using only qualitative data limits usefulness.
Digital image analysis has potential to alleviate these problems. However, some fundamental experimental work is needed first with laboratory-prepared standards of known composition. To ensure reliability of analyses of archaeological ceramics of unknown original recipes, protocols first must be tested for accuracy with laboratory-prepared specimens having additives of known composition, size, and amount, and fired under known conditions.
The primary focus of this research, then, is to calibrate protocols for analysis of digital images of thin sections viewed under a polarizing microscope. Additional experiments will use images obtained by scanning whole thin sections under low magnification. An advantage is that these images include the entire area of the thin section rather than just a single field of view as under a microscope, facilitating macrotexture studies. Some exploratory work also will involve digital images of sherds themselves, to obtain quantitative data that supplements thin-section studies. An advantage is that the time and expense of thin-section cutting, mounting, and grinding are eliminated, allowing data to be collected on even larger numbers of specimens for rapid characterization of some features of a sherd.
For all three of these approaches, using laboratory-prepared specimens as known standards is crucial for development of reliable protocols. In the final phase of research the protocols will be applied to archaeological specimens that have already been well characterized by relevant comparative techniques of analysis. Applying the finished protocols to archaeological samples will allow editing, refinement, and clearer explanations where needed so that the protocols are more widely usable and reproducible.
The intellectual merit of this research is that it will result in new, modernized procedures for quantitative polarized light microscopy of ceramics. The broader impact of the study is that ceramic materials are found at archaeological sites throughout the world. These materials represent objects of a wide range of functions and serve as important markers for understanding many cultural issues about the past. This research will provide the basis for new methods of analyzing and understanding these materials, so that questions about humanity's past can be explored more fully. Students from several disciplines will participate in the project to enhance their laboratory training and ability to work together across different fields while increasing their knowledge about ceramics, one of the most important cultural materials in human history.
Image analysis uses computer software to derive quantitative data from images. In this project we used images of archaeological ceramic sherds. Small samples from sherds were prepared as thin sections (mounted on a glass microscope slide and ground down to 30 microns thickness). The digital images were taken by a microscope camera and via a film scanner. Image analysis then provided data on many size and shape characteristics for each component of the ceramic. The purpose of the analysis was to obtain information relating to raw materials, fabrication methods, and firing processes of archaeological ceramics. This type of information is important because ceramic materials are found at archaeological sites all over the world, represent objects of a wide range of functions that were made and used by diverse groups of people, and can help us better understand the past. Choices in ceramic materials and production techniques reflect the ideas and relationships of people of the past. Identifying when and how technological innovations and change occurred in the past may also help society to better support the conditions leading to innovation and change in the present. The project succeeded in developing a fast and reliable image analysis protocol for achaeological ceramics that modernizes a traditional and proven technique for using low-cost optical microscopy to characterize and interpret ceramic materials. The protocol was developed using over 100 laboratory-prepared specimens of known composition. Variations on the protocol were then developed for more complex archaeological samples. This protocol and its variations were fully tested with a large number of archaeological ceramics ranging from historic bricks from Delaware to high-fired glazed ceramics from Song Dynasty, China. While the full experimental details are being published in professional journals, an image database was also produced to make original images used for the experimental study easily accessible to any interested person. This database is available in the University of Delaware's Institutional Reposity, UD Space. The images can be downloaded by anyone who wants to develop their own image analysis capabilities. During this project, students who had previously never worked in a laboratory setting were able to gain experience with scientific research. The University of Delaware's Laboratory for Analysis of Cultural Materials also developed the capacity to incorporate cutting-edge imaqe analysis techniques along with more traditional procedures of thin-section analysis, permitting a more sophisticated approach to interpreting archaeological ceramics. These new capabilities have sparked new collaborations with archaeological researchers, and we are now routinely applying these techniques to a growing body of archaeological materials. The results of these efforts are helping us use ceramics, a widely occurring archaeological material, to more fully explore questions about humanity’s past.
