There are two commonly used methods of analyzing ceramics in thin-section. Modal analysis, or standard point counting, is preferred by many because it allows the modes (volumetric percentage) of identified rocks and minerals to be calculated with precision (Chayes and Fairbairn 1951; Chayes 1954; Heidke, Miksa and Wallace 2001; Lombard 1985; Middleton et al. 1985 ). In standard point counting a two- dimensional equidistance grid is first established, typically at an interval equal to or greater than the diameter of the largest inclusion in the thin-section. This procedure prevents single grains from being counted multiple times and further allows the reliability of the results to be calculated (e.g. ±5%) at a 95% confidence interval (2s) using the Van Der Plas and Tobi (1965) method. This is the technique used for our Basic and Advanced Ceramic Paste Characterization services (see Petrographic Services).
The second technique, or rather group of related techniques, is grain frequency counting, of which there are three approaches (Dickinson 2001; Middleton et al. 1985). The first is areal counting where a thin section is gradually moved below the crosshair eye-piece and all grains that fall completely within the field of view are identified, measured and counted. Second, is the ribbon (traverse) method where all inclusions that pass completely within a predefined transect, measured by the reticle in the microscope eyepiece, are size-graded, identified and tallied. Lastly is line counting where all grains that are intersected by the horizontal reticle are measured, identified and counted. Frequency counts do not produce volumetric estimates of grain proportions, but are quickly performed and comparable (Dickinson 2001). Moreover, ceramics with sparse and/or large (>.5 mm) inclusions cannot be economically analyzed by point-counting because the total number of identified inclusions is too small to allow for statistical comparisons. For instance, only 200 points can be counted on a thin-section of a sherd that has a maximum inclusion size of 2 mm. If the sample has a large volume of inclusions, say 25%, then only 50 inclusions could be counted for an optimal 20 mm x 40 mm sized thin-section. Similarly, a sample with only 5% very-fine to medium-sized inclusions would require a grid spacing of .5 mm and 2,000 counts in order to identify only 100 inclusions. Given these limitations, traverse counting is our preferred method for resource provenance studies.
Both techniques produce similar and replicable results for well-sorted sands. However, results of the two methods may differ significantly for poorly sorted sands (Dickinson 2001; Middleton et al. 1985), a problem that can be obviated by a research design focusing solely on certain grain sizes. Other methodological parameters can be altered, such as simply ignoring large grains during modal analysis allowing more points to be counted on a thin-section, or using a grid that is not equidistant. We encourage prospective customers to contact us with questions and concerns and assist us in devising an appropriate research design.