International audienceThe mechanical characteristics of various sedimentary stones significantly depend on the water content, where 70% loss of their mechanical strengths can be observed when saturated by water. Furthermore, the clay fraction has been shown to be a key factor of their hydro-mechanical behaviour since it governs for instance the hydric dilation. This work aims at investigating the correlations between the clay minerals content and the mechanical weakening experienced by limestones when interacting with water. The experimental characterization focuses on five different limestones that exhibit very different micro-structures. For each of them, we present the determination of clay minerals composition , the sorption isotherm curve and the dependences of tensile and compressive strengths on the water content. It emerges from these results that, first, the sorption behaviour is mainly governed by the amount of smectite layers which exhibit the larger specific area and, second, the rate of mechanical strength loss depends linearly on the sorption capacity. Indeed, the clay fraction plays the role of a retardation factor that delays the appearance of capillary bridges as well as the mechanical weakening of stones. However, no correlation was evidenced between the clay content and the amplitude of weakening. Since the mechanisms whereby the strength decreases with water content are not clearly established, these results would help to discriminate between various hypothesis proposed in the literature

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Multi-isotope fingerprinting (sulphur, oxygen and strontium isotopes) has been tested to study the provenances of medieval and Renaissance French and Swedish alabaster artwork. Isotope signatures of historical English, French and Spanish alabaster source quarries or areas reveal highly specific, with a strong intra-group homogeneity and strong inter-group contrasts, especially for Sr and S isotopes. The chosen combination of isotope tracers is a good basis for forensic work on alabaster provenance allowing verification of hypotheses about historical trade routes as well as identification of fakes and their origin. The applied analytical techniques of continuous flow isotope ratio mass spectrometry (CF-IRMS) and thermal ionisation mass spectrometry (TIMS) only require micro-samples in the low mg range thus minimising the impact on artwork.

From the first experiments of Lavalle in 1853, it has been concluded, following Taber and Correns's publications, that a growing crystal can exert a linear pressure. This pressure has long been accounted for the stone degradation by salt crystal, as observed on cultural heritage objects. Nevertheless, according to both Riecke's principle and crystal growth theories, a mechanically constrained crystal has a higher solubility than an unstressed one; since the local supersaturation is reduced, the loaded faces may dissolve whereas the crystal still grows along the unloaded faces. In view of these contradictory predictions, we performed new experiments of loaded KCl crystal growth under strictly controlled conditions, with accurate measurement devices. We show that (1) the loaded crystal immersed in a slightly supersaturated solution dissolves along the loaded faces and grows along the unloaded ones, (2) the dissolution rate depends on the topology of the loaded face, and (3) the crystal is not able to grow against any applied pressure nor to develop any "crystallization pressure". These results verify Riecke's principle and contradict Taber's and Correns conclusions and related experiments. Therefore we also discuss the artifacts which were identified during our experiments and have not been monitored in these reference works.