A new method for facilitating tree-ring measurement on charcoal form archaeological and natural contexts

For the past 20 years, the application of dendrology to charcoal fragments found in an archaeological context has encountered the problem of the fragility of the material for its routine development. Friability and fragmentation are among the reasons for the difficulty of the dendrochronological approach. In order to meet this restrictive element, we present a new method in this article and assess its feasibility. The fixing of charcoal by means of a thermo-shrinking sheath makes it possible to preserve it from the risks of destruction during the various stages from sampling to storage. This constriction using a sheath makes it possible to polish the whole of the transversal plane of a flat surface, thus facilitating measurement of the growth ring characteristics. The feasibility was tested on 95 samples of charcoal, corresponding to eight ligneous taxa sampled in different archaeological contexts. A series of tree-ring widths was measured on 80 pieces of charcoal. The synchronicity between the radii of the same piece of charcoal was excellent, only three samples possessing radii with a Gleichlaufigkeit index (Glk) < 70. Of the 14 floating chronologies established on the basis of this data, in eight of them, > 50% of the body demonstrated very good concordance (Glk > 70), making it possible to validate the method on several pieces of charcoal originating from the same context. Thus, thanks to the sheath, the initial condition of the charcoal was preserved and fixed in time. The flat surface created made it possible to take reliable measurements of the rings in the charcoal and these were comparable to the methods normally used in dendrochronology on wood. The ease of manipulation opens up the possibility of applying the dendrological approach to numerous anthracological studies in archaeological and paleo-ecological contexts.