Anthracology in archaeology to identify wood species

Carbon-14 dating is not the only scientific technique used in archaeology. Archaeometry brings together many other investigative and dating techniques. Anthracology is a method practiced by CIRAM laboratories. For complete results, we study charcoal and identify wood species. Anthracology is one of the pillars of archaeobotanical studies, enabling us to understand how ancient human societies used materials. Anthracology also reveals the origin of wood samples, enabling us to differentiate between heartwood, branches and twigs. This helps to overcome the "old wood" effect for carbon-14 dating.

Strict protocol and sophisticated equipment for anthracological study

Anthracological study requires a meticulous sample preparation protocol. After refreshing surfaces with a razor blade, anatomical analysis of charcoal is carried out along three axes; transverse, tangential and radial. Observation of anatomical elements in all three dimensions enables determination of family and genus, and more rarely species.

Observations are made using a stereomicroscope (Olympus® SZ61 binocular loupe) and a dark-field metallographic microscope (Olympus® BX53M), under so-called "natural" light (calibrated white light), coupled with digital cameras.

Characterization of coals is carried out by recording the following information:

CRIAM laboratories offer charcoal characterization through precise analysis and by recording objective data such as:

1 - the presence of bark and pith: by simultaneously observing these two elements on a sample, we deduce stem calibration.

2 - Reaction wood (characteristic of small branches or leaning trunks). This criterion, combined with strong curvature, indicates that we're dealing with a small branch.

3 - The presence of thylls: thylls form in the vessels of some hardwood species, during the formation of heartwood. The presence of thylls helps us to determine potential species, but also gives an indication of the sampling location.

4 - The presence of fungal hyphae: filaments can be found in the vessels. They correspond to the hyphae of fungi growing under aerobic conditions on the surface of a dead or dying tree only at high temperatures (summer season) and humidity levels of between 70 and 90%. The presence of hyphae gives us valuable information on the state of the wood prior to combustion.

5 - Degradation by insects or perforating worms: the presence of galleries in coals is evidence of an attack by insects or perforating glasses. Charred organisms can be found in these galleries. This is proof that the wood was dead and worm-eaten before it was burnt. In some cases, the sapwood of a living subject can be attacked by such organisms.

6 - The presence of radial shrinkage cracks and vitrification: wood saturated with water will show a large number of shrinkage cracks. Vitrification is a complex phenomenon occurring during combustion. Aspects of vitrification depend on the nature of the wood (species, size, moisture content) and combustion conditions (temperature and oxygenation conditions). We will distinguish 4 aspects of vitrification corresponding to 4 levels of carbonization:

• Dull appearance (level 0): coals have a dull appearance, gray or black in color. The anatomical structure is preserved.
• Glossy appearance (level 1): coals are dark gray to light in color and very shiny.
• Melted appearance (level 2): surfaces are very shiny and the anatomical structure is no longer discernible.
• Scoriaceous aspect (level 3): this is the last degree of vitrification, in which the coals are completely destructured.

7 - Grading: analysis of the curvature of the growth rings and the angle of the wood rays will enable us to identify the part of the tree from which the coals come. Charcoal will be classified according to 4 categories:

• Rings with strong curvature: indicates very small-gauge wood
• Rings with moderate curvature
• Rings with weak curvature: indicates the use of large-gauge wood (large branch or trunk)
• Rings with indeterminate curvature

8 - Growth ring width and growth rate. A narrow ring width indicates slow growth (unfavorable growing conditions or old age). Whereas wide growth ring widths indicate strong growth (very favorable conditions or young subject). The rate of growth, i.e. the regularity of ring widths, indicates whether the subject has grown homogeneously or whether there have been events that have temporarily hindered growth (climatic conditions, fungal attack, tree injuries...).

9 - Traces of woodworking: grooves/scratches on the surface may attest to work carried out on the wood using tools.

For each archaeological site referenced, a systematic analysis of all charcoals will be carried out according to the criteria mentioned above. The data will be compiled in the form of tables and graphs and reported in an analysis report.

CIRAM, specialists in carbon-14 dating and archaeomaterial analysis, offers the meticulous examination of your wood and charcoal. To deliver relevant and accurate results, we comply with current international standards.