Study of organic residues

Fourier transform infrared spectroscopy (FTIR), used in ATR mode or under microscopy, is an essential analytical technique for identifying the major families of organic compounds in archaeological materials. This method enables the presence of lipids, waxes, natural resins or proteins to be detected on the basis of characteristic spectral signatures.

However, the presence of mineral matter can generate spectral interference, making the identification of organic compounds more delicate. To overcome this limitation, FTIR is generally used as a preliminary technique. CIRAM specialists integrate it into multi-technique analytical protocols, in association with chromatography or Raman spectroscopy, to refine the identification of organic residues.

Gas chromatography-mass spectrometry (GC-MS) is a benchmark technique for analyzing organic compounds in archaeology. This technique is based on the separation of molecules present in a sample using gas chromatography (GC), followed by precise identification of constituents by mass spectrometry (MS), according to their mass-to-charge ratio.

This method enables trace compounds to be detected and quantified, providing essential information on their chemical composition.

CIRAM's experts identify specific biomarkers, enabling them to reconstruct the nature of ancient substances such as vegetable oils, animal fats, tannins and tars. This expertise contributes to the interpretation of the cultural and economic practices of ancient societies, by revealing the uses and transformations of organic matter over time.

Mainly used to analyze mineral materials, Raman spectrometry is nevertheless a valuable complementary technique for archaeometry. Its main advantage lies in its non-destructive nature, enabling samples to be studied without prior alteration or preparation.

Thanks to its excellent spatial resolution, this method makes it possible to analyze organic residues on a microscopic scale (of the order of a few microns). CIRAM researchers integrate Raman spectrometry into multimodal analysis protocols, coupling it with FTIR spectroscopy and GC-MS chromatography. This combined approach is essential for the characterization of complex substances and enables the precise identification of organic materials used by past societies.

Carpology is the study of seed and fruit remains from archaeological contexts such as vessels or sediments. Analysis of these plant macro-remains provides valuable information on agriculture, diet and the exploitation of plant resources by ancient societies. Even charred, these seeds can be identified by CIRAM scientists to reconstruct past environments.

Palynology, which focuses on the study of pollen and spores, complements carpology and anthracology. anthracology (study of charcoal) in the reconstruction of ancient landscapes and climates. Analyses carried out by CIRAM, via optical and electron microscopy, enable pollen grains to be identified according to their morphology and structure, thus refining paleoenvironmental models and the dynamics of land occupation.