Chemical imaging techniques for the analysis of complex mixtures: New application to the characterization of ritual matters on African wooden statuettes

Chemical imaging techniques, based on the combination of microscopy and spectroscopy, are well suited to study both the composition and the spatial organization of heterogeneous complex mixtures of organic and mineral matter. Time-of-flight secondary ion mass spectrometry (ToF-SIMS), followed by scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) and Fourier transform infrared microscopy (FTIR microscopy) have been applied to non-destructive analysis of micro-samplings of ritual matters deposited on the surface of African wooden statuettes. With a very careful preparation, using ultramicrotomy on embedded samples, it was possible to perform successively all the measurements on a single fragment. Comparison and superposition of the different chemical images, obtained on a sample from a significant actual artefact, have allowed us to identify minerals (clays, quartz and calcium carbonate), proteins, starch, urate salts and lipids and to map their spatial distribution.