WOOD CHARCOAL : RECOGNITION
Once collected from the field charred material is sorted and identified in the laboratory. Sorting and sub-sampling are a step common to the study of all charred archaeobotanical macroremains (wood charcoals, seeds, fruits, roots and tubers). It is useful to assess the richness of each sample through rapid scanning to determine which samples are worth further investigation.
If flots are very large or rich in plant macroremains, it may be necessary to subsample. Saturation curves have been used to determine the optimal number of fragments to identify for a set of samples (Chabal 1997), and the amalgamation of several samples from the same context can increase overall sample size (Badal Garcia 1992). Van der Veen and Fieller (1982), however, have shown statistically that a sample of c.500 items is sufficient to estimate the relative proportions of different taxa with an accuracy of +5% and a reliability of 95-98%. Subsampling is therefore justified if the number of wood charcoal fragments, seeds or chaff fragments, is greater than c.500. Different sizes of sample may be sorted for different categories of charred remains. Often the coarse (>1mm) flot is sorted in its entirety while the fine flot (<1mm) is subsampled. An unbiased subsample can be achieved using a riffle box (Van der Veen and Fieller 1982).
The remains in the smaller subsample must be ‘multiplied up’ before combining the counts with those of the larger subsample. It is therefore best if the fractions sorted for each mesh size are not too dissimilar, so that the number by which the remains in the smaller fraction are multiplied is not too great.
Sorting involves the extraction of identifiable plant remains from the general flot matrix; at the same time different categories of plant material (seeds, wood, parenchyma, dung) can be separated. To make sorting easier, it may be helpful to dry sieve the coarse flot into different size categories (e.g. 1-2mm, 2-3mm, 3-4mm, >4mm). Sorting may be carried out under a low-power stereomicroscope, generally at about x10 to x20 magnification. Sorting should proceed systematically, starting at one end of the sample and passing each fragment before the eye (with a fine paintbrush) to determine whether or not it should be extracted. This method of sorting (Zalucha 1982, Asouti and Hather 2001) is preferable to picking out the larger pieces from the main body of the sample (Miller 1985) which usually results in a biased sample of plant types. Wood charcoal is usually removed only from the greater than 2mm fractions.
Wood charcoal can be distinguished from other archaeobotanical macroremains because it looks either like small twigs or is in the form of rectangular/cuboid shapes with parallel (linear) lines. Whole seeds are easily recognised; fragments of seeds and fruit stones are usually smooth on some part of their surface and are often porous internally. Fragments of roots and tubers can be distinguished by their cellular internal structure, and occasionally a dull portion of the surface, perhaps with the bases of rootlets.
- Sieves (4.0, 2.0, 1.0, 0.3mm)
- Riffle box
- Light source
- Petri dishes
- Fine paint brush
- Soft tweezers
- Containers (tubes, gelatine capsules, sealable bags)
- Identification tags
- Asouti, E., Hather, J. (2001). Charcoal analysis and the reconstruction of ancient woodland vegetation in the Konya Basin, south-central Anatolia, Turkey : results from the Neolithic site of Çatalhöyük East. Vegetation History and Archaeobotany 10: 23-32.
- Badal Garcia, E. (1992). L'anthracologie préhistorique : à propos de certains problèmes méthodologiques. Bulletin de la société botanique de France. Actualités botaniques 139 (2/3/4): 167-89.
- Chabal, L. (1997). Forêts et sociétés en Languedoc (Néolithique final, Antiquité tardive) : l'anthracologie, méthode et paléoécologie. Documents d'Archéologie Française 63.
- Miller, N. (1985). Paleoethnobotanical Evidence for Deforestation in Ancient Iran : a case study of urban Malyan. Journal of Ethnobiology 5/1: 1-19.
- Van der Veen, M. and Fieller, N. (1982) 'Sampling seeds', Journal of Archaeological Science 9 pp. 287-298.
- Zalucha, L. (1982). Methodoloy in Paleoethnobotany; A Study in Vegetational Reconstruction Dealing with the Mill Creek Culture of Northwestern Iowa. Unpublished PhD Thesis. University of Wisconsin.