Calibration and Visualization of Wall-Thickness and Porosity Distributions of Ceramics Using X-radiography and Image Processing

Abstract

It has been reported that X-radiography studies of archaeological ceramics can be used to identify fashioning processes. However, diagnostic criteria used for such interpretations often appear unconvincing to the non-specialist. The qualitative nature of the interpretations is a significant factor in this quality assessment. Published reproductions of X-radiographs rarely clearly demonstrate the structural patterns observed and described. It is possible to describe quantitatively features in X-radiographs that are indicative of particular fashioning techniques. Unfortunately, this usually requires access to digital X-ray equipment. A method is described here for acquiring and calibrating digital images from X-radiographs exposed onto standard film. Often with ceramics, thickness and density information are confounded in X-radiographs. A low-pass filtering technique is used to remove the density information. The resulting image is then calibrated using Lambert's Law of X-ray absorbtion combined with some simple measurements to produce a sherd thickness map. The filtered density information is then similarly treated to drive a density distribution across the sherd. The use of the technique is illustrated on three specimens from an experiment in which the fashioning techniques were carefully controlled. Enhanced images are used to document features which distinguish the three fashioning techniques. Measurement of such features and quantitative interpretation of wall thickness of ceramics are highlighted as research areas which require further attention.