A comparative analysis of wet and dry ashing techniques for the extraction of phytoliths from plant material

Two methods are commonly used for the extraction of phytoliths from plant material to be used as reference in the analysis of archaeological phytolith samples: (1) spodograms or dry ashings; and (2) acid digestions or wet ashing. It has been suggested that these techniques may modify the resultant samples in different ways. Dry ashing, in particular, has been implicated as a cause of shrinkage and warping in phytolith assemblages when incineration occurs at ≥450°C. The results of a morphometric comparative analysis between the dry ashing and wet ashing methods do not support these claims. This study establishes that differences in patterns of dimension and curvature of short bilobate phytoliths and of elongate phytoliths both subjected to dry and wet ash preparation are not statistically significant. There is, therefore, no detectable evidence of morphological impact as a result of these methods. This finding implies that any differences that do occur in phytolith size and curvature are typical, possibly random permutation within assemblages, or that they are the result of variation in leaf cell structure rather than the consequence of a particular extraction procedure. This suggests that the practice of using different methods of preparation of reference samples for fossil analysis can be reliably continued.