The charcoal discovered during archaeological excavations is not only used for carbon-14 dating. Indeed, their study also makes it possible to identify wood species, reconstruct ancient landscapes, and better understand the practices of past societies. This discipline, called anthracology, relies on the meticulous observation of the anatomical structures of charred wood.

Discover how laboratories analyze archaeological coals and what scientific information they obtain from simple charcoal fragments.

How does an anthracological analysis take place?

Anthracological study requires a meticulous sample preparation protocol. After refreshing the surfaces with a razor blade, the anatomical analysis of charcoal is carried out along the three axes: transverse, tangential, and radial. Thanks to this three-dimensional observation, scientists can determine the family and genus, and more rarely the species.

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

What anthracological criteria are analyzed?

Beyond identifying species, an anthracological study involves observing numerous anatomical criteria. These observations allow for the characterization of charcoal, the reconstruction of the wood's history before its combustion, and a more refined interpretation of archaeological contexts.

These observations are not based solely on the anatomical identification of the wood. Archaeobotanists also study several indicators that allow them to trace the history of the wood before and during its combustion.

Identify the origin and the part of the tree used

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

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

• Calibration assessment: analyzing the curvature of growth rings and the angle of woody rays will identify the part of the tree from which the charcoal originated. Charcoal is classified into 4 categories:

High curvature dark circles	Indicate very small caliber woods
Dark circles with moderate curvature
Low curvature dark circles	Indicates the use of large-caliber wood (thick branch or trunk)
Rings with indeterminate curvatures

To determine the state of the wood before burning it.

• The presence of tyloses: tyloses form in the vessels of some hardwood species during heartwood formation. The presence of tyloses helps us to determine potential species, but also to indicate the location of the sample.

• The presence of fungal hyphae: filaments can be observed in the vessels of charcoal. They indicate the development of fungi in the wood before its combustion, particularly during the degradation phases of a dead or dying tree. Their observation thus provides information on the state of the wood before its use.

• Degradation by boring insects or worms: similarly, the presence of galleries in coals is proof of an attack by boring insects or worms. It is possible to find the carbonized organisms in these galleries. These clues are proof that the wood was dead and rotten before its combustion. In some cases, the sapwood of a living subject can be attacked by such organisms.

Analyze the combustion conditions

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

Matte finish (level 0)	The coals are matte in appearance, gray or black in color. The anatomical structure is preserved.
Shiny aspect (level 1)	The coals are dark gray to light gray in color and very shiny.
Melted aspect (level 2)	The surfaces are very shiny and the anatomical structure is no longer discernible.
Scoriaceous appearance (level 3)	This is the highest degree of vitrification for which the coals are totally unstructured.

Study of wood growth and its use

• The width of the growth rings and growth rate. A narrow width indicates that the wood grew slowly (unfavorable growing conditions or an old subject). Conversely, wider rings indicate greater growth, linked for example to favorable environmental conditions or a younger tree. Therefore, the growth rate, i.e., the regularity of the ring widths, indicates whether the subject grew uniformly or if there were events that temporarily hindered growth (climatic conditions, fungal attack, tree injuries, etc.).

• Woodworking traces: surface grooves/scratches can attest to work done on the wood using tools.

Why are these observations important?

For each archaeological site referenced, a systematic analysis of all charcoal is carried out according to the criteria mentioned above. The data compiled in tables and graphs then allows for the drafting of an analysis report.

Anthracological analysis therefore does not consist solely of identifying a wood species. By observing the anatomical characteristics and alterations of the charcoal, specialists reconstruct the origin of the samples, the combustion conditions, and the history of the woods used. This information enriches archaeological interpretation and allows for the selection of the most relevant samples before potential carbon-14 dating.

To understand how anthracology improves the reliability of carbon-14 dating, also consult our article on the role of anthracology in preventive excavations.