Unexpected materials in a Rembrandt painting characterized by high spatial resolution cluster-TOF-SIMS imaging.

The painting materials of the Portrait of Nicolaes van Bambeeck (Royal Museums of Fine Arts of Belgium, Brussels, inv. 155) painted by Rembrandt van Rijn in 1641 has been studied using high resolution cluster-TOF-SIMS imaging. In the first step, a moderate spatial resolution (2 µm) was used to characterize the layer structure and the chemical composition of each layer on account of a high mass resolution. Then, in the second step, and despite a low mass resolution, the cluster primary ion beam was focused well below 1 µm in order to reveal smaller structures in the painting sample. The study confirmed the presence of starch in the second ground layer, which is quite surprising and, at least for Rembrandt paintings, has never been reported before. TOF-SIMS also indicated the presence of proteins, which, added to the size and shape of lake particles, suggests that it was manufactured from shearings (waste of textile manufacturing) of dyed wool, used as the source of the dyestuff. The analyses have also shown various lead carboxylates, being the products of the interaction between lead white and the oil of the binding medium. These findings considerably contribute to the understanding of Rembrandt's studio practice and thus demonstrate the importance and potential of cluster-TOF-SIMS imaging in the characterization on a submicrometer scale of artist painting materials.

Palaeoproteomics gives new insight into early southern African pastoralism.

The advent of domestication is a major step that transformed the subsistence strategies of past human societies. In Africa, domestic caprines (sheep and goat) were introduced in the north-eastern part of the continent from the Near East more than 9000 years ago. However, their diffusion southwards was slow. They are thought to have made their first appearance in the southern part of the continent ca. 2000 years ago, at a few Later Stone Age sites, including Leopard Cave (Erongo region, Namibia), which provided the oldest directly dated remains assigned to sheep or goat on the basis of morphology of bones and teeth. However, similarities in morphology, not only between these two domesticated caprine species, but also between them and the small wild antelopes, raised questions about the morphological species attribution of these remains. Additionally, the high fragmentation of the site's osteological remains makes it difficult to achieve species-level taxonomic identification by comparative anatomy. In this paper, we report molecular species identification of the Leopard Cave remains using palaeoproteomics, a method that uses protein markers in bone and tooth collagen to achieve taxonomic identification of archaeological remains. We also report new direct radiocarbon dates. Wild antelope remains from museum collections were used to enrich the available protein record and propose de novo type I collagen sequences. Our results demonstrate that the remains morphologically described as domesticates actually belong to a wild antelope species and that domestic caprines first appeared at Leopard Cave 1500 years later than previously thought. This study illustrates that the use of palaeoproteomics coupled with direct radiocarbon dates is particularly suited to complement classic zooarchaeological studies, in this case concerning the arrival of the first herding practices in arid environments.

Tracking the Near Eastern origins and European dispersal of the western house mouse.

The house mouse (Mus musculus) represents the extreme of globalization of invasive mammals. However, the timing and basis of its origin and early phases of dispersal remain poorly documented. To track its synanthropisation and subsequent invasive spread during the develoment of complex human societies, we analyzed 829 Mus specimens from 43 archaeological contexts in Southwestern Asia and Southeastern Europe, between 40,000 and 3,000 cal. BP, combining geometric morphometrics numerical taxonomy, ancient mitochondrial DNA and direct radiocarbon dating. We found that large late hunter-gatherer sedentary settlements in the Levant, c. 14,500 cal. BP, promoted the commensal behaviour of the house mouse, which probably led the commensal pathway to cat domestication. House mouse invasive spread was then fostered through the emergence of agriculture throughout the Near East 12,000 years ago. Stowaway transport of house mice to Cyprus can be inferred as early as 10,800 years ago. However, the house mouse invasion of Europe did not happen until the development of proto urbanism and exchange networks - 6,500 years ago in Eastern Europe and 4000 years ago in Southern Europe - which in turn may have driven the first human mediated dispersal of cats in Europe.

Cluster TOF-SIMS imaging of human skin remains: analysis of a South-Andean mummy sample.

A skin sample from a South-Andean mummy dating back from the XI(th) century was analyzed using time-of-flight secondary ion mass spectrometry imaging using cluster primary ion beams (cluster-TOF-SIMS). For the first time on a mummy, skin dermis and epidermis could be chemically differentiated using mass spectrometry imaging. Differences in amino-acid composition between keratin and collagen, the two major proteins of skin tissue, could indeed be exploited. A surprising lipid composition of hypodermis was also revealed and seems to result from fatty acids damage by bacteria. Using cluster-TOF-SIMS imaging skills, traces of bio-mineralization could be identified at the micrometer scale, especially formation of calcium phosphate at the skin surface. Mineral deposits at the surface were characterized using both scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy and mass spectrometry imaging. The stratigraphy of such a sample was revealed for the first time using this technique. More precise molecular maps were also recorded at higher spatial resolution, below 1 µm. This was achieved using a non-bunched mode of the primary ion source, while keeping intact the mass resolution thanks to a delayed extraction of the secondary ions. Details from biological structure as can be seen on SEM images are observable on chemical maps at this sub-micrometer scale. Thus, this work illustrates the interesting possibilities of chemical imaging by cluster-TOF-SIMS concerning ancient biological tissues.

Cavitation in heavy water and other liquids.

We report on measurements of the cavitation pressure in several liquids subjected to tension in an acoustic wave and compare the results to classical nucleation theory (CNT). This study is motivated by the sizable discrepancy between the acoustic cavitation threshold measured in water and the value predicted by CNT. We find that the same discrepancy is present for heavy water, whereas the agreement is better for ethanol and heptane and intermediate in the case of dimethyl sulfoxide. It is well-known that water is an anomalous liquid, a consequence of its hydrogen-bonded network. The other liquids studied represent very different molecular interactions. Our results indicate that the cavitation threshold approaches the prediction of CNT as the surface tension gets smaller. Conversely, this raises the question of the validity of a simple theory such as CNT to account for high surface tension liquids and suggests that an appropriate microscopic model of such liquids may be necessary to correctly predict the cavitation threshold.