Yellow goethite (or-FeOOH) and red hematite were used as pigments by Palaeolithic painters. When heated, goethite dehydrates and transforms to hematite. Archaeologists wonder whether prehistoric people knew of this property and used it. We present a way to distinguish heated goethite from natural hematite. The methods used are X-ray diffraction and transmission electron microscopy. A double 'signature', namely selective broadening of diffraction rejections and porous nanostructure, is evidenced in heated goethite. Coupled with mineralogical associations, this allows us to establish a procedure to investigate the natural or artiJcial origin of hematite samples. Applied to the Palaeolithic site of Troubat, it reveals no difference between the Magdalenian and Azilian cultures concerning the heat-treatment of pigments; an area specializing in heat-treating pigments may, nevertheless, have existed inside the cave, which would indicate that heating was deliberate.

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We propose an original method based on both proton nuclear magnetic relaxation dispersion and high-resolution NMR spectra to investigate the microstructure of synthesized Ca3SiO5-hydrated cement paste. This method allows a clear assessment of the local proton chemical sites as well as the determination of dynamical information of moving proton species in pores. We show also how the microstructure evolves during and after completion of hydration in a range of length scales between 2 and 500 nm. In particular, we show how the pore size distribution of the cement paste reaches progressively a power-law characteristic of a surface-fractal distribution with a dimension Df = 2.6, which takes into account the hierarchical order in the material. Last, we study how this pore size distribution is modified during setting by varying either the water-to-cement ratio or addition of ultrafine particles. This shows that our method could be relevant to relate the mechanical properties to the microstructure of the material. This proposed NMR method is general enough for the characterization of microstructure of any porous media with reactive surface involving water confinement.

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