An artifact used for the preparation of starchy foods is likely to retain some of the residues associated with use on its surface. The processing of tubers, fruits, seeds, or roots generally results in the accumulation of starch and associated material (e. g., raphides, other cellular material) on most of the tool surface. Material that has been heavily impacted onto the surface (through pounding or grinding) is more likely to survive. In general, the survival of material occurs on or near the used surfaces/edges and in imperfections in the tool surface (see Organic Residue Analysis).
Preliminary microscopic examination (low and high power) and documentation of residues is essential, prior to extraction and processing. Microscopic examination provides information about the location and type of residues present on the artifact. Starch granules, distinctive by their birefringence and extinction cross under polarizing filters, can easily be observed at this stage. The isolation of starch residues should also be undertaken with consideration to other residues that may also be present on the tool surface or edges. For example, the study of phytoliths from a tool surface has the potential to provide strong supporting evidence for the interpretations drawn from starch analysis. Other related plant material, such as fragments of xylem and phloem or raphides, may also be preserved on the artifact surface. If the tool was a multifunctional item, residues of blood, hair, or feathers may also be present (see Blood Residue Analysis). It is extremely advantageous to tailor the extraction procedure for the maximum recovery of residues from an artifact surface.
Following microscopic documentation of an artifact, the residue can be extracted from the tool surface for more detailed study. Analysis can proceed by employing ‘whole tool’ extraction techniques, or by targeting specific areas on the artifact surface, thereby conserving some of the residue. The samples are then processed using heavy liquid and centrifugation to isolate the starch granules from the original sample.
It is essential to verify that the residues analyzed are the original remnants of processing in antiquity and do not represent contamination from the surrounding depositional matrix. An analysis of the sediments both close to and distant from the artifact studied and from the unused surfaces may influence the interpretation of results. This is why a hierarchical approach (microscopy, documentation, extractions, etc.) to the study of residues is so important and that sound positive and negative experimental controls are incorporated into any research design.
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