Archaeology

CESAAR laboratory propose dating and characterization of your archaeological artefacts.

Radiocarbon dating

Radiocarbon dating enable to date organic materials such as wood, paper, plant fibers, ivories...

The AMS technique (particles accelerator mass spectrometry) requires just a few milligrams of material for highly accurate results.

The method is based on the radioactive decay curve of carbon-14. During the life of an organism, the proportion of radiocarbon it contains in relation to total carbon is in equilibrium with the proportions in the atmosphere. After death, the exchange ceases and the carbon-14 begins to decay at a constant rate. Mesure of the residual carbon-14 quantity, make it possible to obtain the age at which the organism died, generally within a range of more or less 150 years.

14C bomb peak: Carbon-14 can be used to go back as far as 45,000 years BC. From the 17th century onwards, the calibration of radiocarbon dates means that dating intervals are often very wide.
For recent periods, from 20th century onwards, it is nevertheless possible to determine whether the death of the organism occurred before or after the nuclear tests of the 1950s and 60s. This method known as the « bomb peak » can be used to provide a certificate of age in case of protected species for example.

Calibration curve of a wood sample from an Egyptian sculpture dating from the Late Period: 40.4% probability that the wood was felled between 390 and 352 BC and 55.1% probability between 290 and 209 BC.

Thermoluminescence

Thermoluminescence age tests can be used to date earthenwares and ceramics.

Thermoluminescence is based on an ingenious principle: the crystals contained in earthenwares (quartz, feldspars) have the ability to accumulate energy over the time. When heated, these crystals release this energy in the form of light, a phenomenon known as thermoluminescence. This light emission is directly linked to the time elapsed since the object was last fired.

Thermoluminescence curves of a terracotta from the Ban Chiang culture. The average age of the last firing is between 1800 and 2400 years.

Storage of Luminous Energy: the quartz and feldspars crystals found in earthenwares and ceramics have the ability to store energy. This energy comes from surrouding natural ionising radiation, such as cosmic rays and radioactive elements in the soil.

Light Emission on Heating: when the object is subjected to a source of heat, for example during its initial firing, the electrons trapped in these crystals are released from their « electron traps ». This release of electrons is accompanied by the emission of light, a phenomenon known as thermoluminescence.

Resetting the "ElectronTraps": after this initial firing, the « electron traps » in the crystals are reset and begin to trap electrons again as a result of continued exposure to the surrounding natural radiation.

Luminescence Measurement: to date the object, a sample of these crystals is heated in a controlled manner in the laboratory. During this process, the trapped electrons are released, emitting light. The amount of light emitted is directly proportional to the time elapsed since the object was last fired. By measuring the intensity of this luminescence, it is possible to date the last time the object was fired.

Wood and charcoal

The study of wood: xylology

From centimeter-sized samples or by direct surface observation of the object, microscopic structures can be examined to identify the wood species.

Anatomical details are revealed using a scalpel, razor and sandpaper, then observed under a stereomicroscope and optical microscope.

Cross-section of a sample of the excelsa species (Iroko) from a Royal Bamoun seat in Cameroon.

The study of charcoals : anthracology

Anthracology is the scientific study of archaeological charcoals. This science provides crucial information about past landscapes and forests, agricultural practices, the environnement and climate change.

When wood is transformed into charcoal, some of the structure and composition of the original wood is preserved. Charcoal samples can be analysed to determine the species, and their proportions in the fireplaces or occupation soils.

The origin of the wood is also identified : small or large branches, center or outside of the trunk, young or old tree.

Wood charcoal can be dated using the radiocarbon dating method, providing an estimate of the age of the sample and, by extension, of the associated archaeological site or context.