STUDY OF ORGANIC RESIDUES

Fourier transform infrared spectroscopy, in ATR mode or microscopy, is a method that our teams of scientists use in the laboratory, in order to identify the major families of organic compounds. For example, we will be able to characterize the presence of oil, animal fat or natural resin for example.

The mineral material will however be able to bring a spurious signal, preventing the identification of the organic compounds present. This is why infrared spectrometry will be used in the approach stage. CIRAM teams will generally couple FTIR spectrometry with other analytical techniques, such as chromatography or Raman spectrometry for example.

Gas chromatography (GC) or liquid chromatography (LC) is the technique dedicated to the study of organic compounds. CIRAM teams typically couple chromatography with mass spectrometry. Chromatography will separate the compounds of a sample, and mass spectrometry, will identify the compounds according to their mass.

From the GC-MS analysis, CIRAM’s doctors and engineers will characterize all the molecules present in a mixture or an archaeological organic residue. It is the nature of these molecules associated with their concentration that will make it possible to trace the material used, olive oil, walnut brou, animal fat, tannin…

Although it is more dedicated to the study of mineral matter, Raman spectrometry is nonetheless an interesting method in archaeometry, as it is non-invasive and does not require any pre-treatment of samples.

Researchers at CIRAM will be able to use Raman spectrometry alone, or in coupling with FTIR spectrometry or GC-MS chromatography. Indeed, the residues found in ancient pottery are so complex, that it is usually necessary to use different complementary analytical techniques.

Carpology is the study of seed and fruit remains found in ancient containers or archaeological sediments. Analysis of these plant residues provides information about human activities and ancestral lifestyles. Even charred, CIRAM scientists are able to identify the nature of these seeds, and thus understand their use and reconstruct environments.

Palynology is the study of pollens and spores released by plant species. When coupled with carpology and anthracology, these techniques will allow the reconstruction of environments and climates. The observations made by our teams of scientists in optical microscopy or electron microscopy will allow us to determine the dimensions and shapes of the pollen or spore grains, the number and shape of the apertures, the ornamentation, the structure of the wall… and thus to define the family, the genus and in the best case the plant species.