Anne-Solenn Le Hô

The nature of the extraordinary finish of Stradivari's instruments.

What is Stradivaris “secret”? The composition of the mythical varnish that coats Stradivaris violins has raised controversial assumptions for the past two centuries. By using a complementary array of analytical tools, the chemical microstratigraphy of these varnishes has been established. The results provide information on the materials and techniques that were used by the Master, with a detailed characterization of the varnish.

Molecular criteria for discriminating museum Asian lacquerware from different vegetal origins by pyrolysis gas chromatography/mass spectrometry

This paper focuses on the identification of several chemical markers of vegetal species of Oriental lacquers with the aim at providing a methodology consistent with sampling restrictions necessarily applied in the field of cultural heritage. The method proposed is based on rapid and easy single step thermally assisted hydrolysis-methylation (THM) pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analysis that can be carried out with a minimum amount of matter (typically 10 μg for a sample collected on a museum or an archaeological object). The main contribution of this study is to provide multiple molecular criteria for discriminating the three Asian species used for making lacquers, namely Rhus verniciflua Stokes, Rhus succedanea and Melanorrhoea usitata. Because these trees grow in specific areas, identifying the species involved in ancient lacquer coatings also provides geobotanical data and fruitful information on the exchange networks and trading routes developed by ancient societies. With this purpose, a systematic study of all pyrolysis products of lacquer coatings was carried out on modern dried lacquer films from authentified provenance. It was demonstrated that the whole pyrolysis products play a significant role in identifying the vegetal species. The chemotaxonomic value of homologous series of alkanes, alkenes and benzene derivatives, rarely explored until now, was assessed. It was shown that the combination of data related to five distinct groups of pyrolytic markers (composition and/or distribution of alkanes, alkenes and benzene, alkenyl-, alkylcatechol and phenol derivatives) provided new strong criteria to establish vegetal origin and provenance of Asian artworks, even though they have been largely altered over time. Case studies of archaeological Chinese lacquered artefacts and Japanese Buddhistic altar were thereafter successfully investigated to address informative potential and efficiency of these criteria on ancient and degraded lacquer coatings.

Microscale imaging of the preservation state of 5,000-year-old archaeological bones by synchrotron infrared microspectroscopy.

AbstractArchaeological bone materials record characteristic markers of life in prehistoric times (dating, climate, environment, diet, human migration) in their isotopic and chemical composition in addition to palaeontological, archaeozoological, anthropological and palaeogenetic information. Thus, the discovery and conservation of archaeological bone materials is of great importance to get access to this information. However, archaeological materials are altered by different postmortem processes and it appears necessary to estimate if the archaeological information is still reliable or if it has been modified during burial. As archaeological bone materials present a high structural hierarchy at the micro- and nanoscale, changes induced by diagenetic phenomena have to be observed at these scales. One method for revealing post mortem changes of the bone structure and composition at the microscale is synchrotron radiation micro-FTIR imaging (SR micro-FTIR). Thus, thin sections of about 5,000-year-old archaeological bones have been analysed in transmission mode at the IRIS beamline (BESSY II, HZB Berlin) to determine markers of the state of bone preservation at the microscale. The archaeological bone material comes from station 19 of the Neolithic site of the Chalain Lake. By using SR micro-FTIR it was possible to image characteristic bone structures, e.g. osteons (the constitutive histological unit of cortical bone), using the absorption band ratios corresponding to different chemical bone constituents (collagen content and quality, phosphate crystallinity, carbonate content). These data allow us to precisely evaluate the state of preservation of a 5,000-year-old bone at the histological level. FigureChemical mapping of a thin section of the archaeological bone AB_CH19nb1 from the Neolithic station 19 at Chalain Lake

Advanced discriminating criteria for natural organic substances of cultural heritage interest: spectral decomposition and multivariate analyses of FT-Raman and FT-IR signatures.

Natural organic substances are involved in many aspects of the cultural heritage field. Their presence in different forms (raw, heated, mixed), with various conservation states, constitutes a real challenge regarding their recognition and discrimination. Their characterization usually involves the use of separative techniques which imply destructive sampling and specific analytical preparations. Here we propose a non destructive approach using FT-Raman and infrared spectroscopies for the identification and differentiation of natural organic substances. Because of their related functional groups, they usually present similar vibrational signatures. Nevertheless the use of appropriate signal treatment and statistical analysis was successfully carried out to overcome this limitation, then proposing new objective discriminating methodology to identify these substances. Spectral decomposition calculations were performed on the CH stretching region of a large set of reference materials such as resins, oils, animal glues, and gums. Multivariate analyses (Principal Component Analyses) were then performed on the fitting parameters, and new discriminating criteria were established. A set of previously characterized archeological resins, with different surface aspects or alteration states, was analyzed using the same methodology. These testing samples validate the efficiency of our discriminating criteria established on the reference corpus. Moreover, we proved that some alteration or ageing of organic materials is not an issue to their recognition.

Identification of the finishing technique of an early eighteenth century musical instrument using FTIR spectromicroscopy.

AbstractThe study of varnishes from musical instruments presents the difficulty of analysing very thin layers of heterogeneous materials on samples most of which are generally brittle and difficult to prepare. Such study is crucial to the understanding of historical musical instrument varnishing practices since written sources before 1800 are very rare and not precise. Fourier-transform infrared (FTIR) spectroscopy and imaging methods were applied to identify the major chemical components within the build-up of the varnish layers on a cello made by one of the most prominent French violin-makers of the eighteenth century (Jacques Boquay, ca. 1680–1730). Two types of FTIR imaging methods were used: scanning with a synchrotron-based microscope and full-field imaging using a 2D imager with a conventional source. An interpretation of the results obtained from these studies on the Boquay cello is that the maker first applied a proteinaceous layer, probably gelatine-based animal glue. He later applied a second layer based on a mixture of a drying oil and diterpenic resin from Pinaceae sp. From an historical perspective, the results complement previous studies by describing a second technique used for musical instrument finishes at the beginning of the eighteenth century in Europe. FigureFTIR spectromicroscopy study of a cello made by the luthier Jacques Boquay (Paris, ca. 1680-1729) shows that the maker first applied a proteinaceous layer, probably gelatine-based animal glue.

Alteration of Asian lacquer: in-depth insight using a physico-chemical multiscale approach.

Oriental lacquer has been used in Asian countries for thousands of years as a durable and aesthetic coating material for its adhesive, consolidating, protective and decorative properties. Although these objects are made from an unusual material in Occident, Western museum collections host many lacquerwares. Curators, restorers and scientists are daily confronted with questions of their conservation and their alteration. The characterization of their conservation state is usually assessed through visual observations. However deterioration often starts at the microscopic level and cannot be detected by a simple visual inspection. Often, ageing and deterioration of artworks are connected to physical, mechanical and chemical transformations. Thus new insight into alteration of lacquer involves the monitoring of macro-, microscopic and molecular modifications, and this can be assessed from physico-chemical measurements. Non-invasive (microtopography and Scanning Electron Microscopy - SEM) and micro-invasive (infrared micro-spectroscopy using a synchrotron source - SR-μFTIR) investigations were performed to study the degradation processes of lacquers and evaluate their level of alteration. In particular, spectral decomposition and fitting procedure were performed in the 1820-1520 cm(-1) region to follow the shift of the C=O and C=C band positions during lacquer ageing. The present work proves the potential of this physico-chemical approach in conservation studies of lacquers and in the quantification of the state of alteration. It evidences chemical phenomena of alteration such as oxidation and decomposition of a lacquer polymeric network. It also demonstrates for the first time the degradation front of artificially aged lacquer and the chemical imaging of a more than 2000 years old archaeological lacquer by using SR-μFTIR.

The Consumption of Bone Powder in the Early Neolithic Societies of Southeastern Europe: Evidence of a Diet Stress?

Research performed on Early Neolithic ceramic assemblages from southwestern Bulgaria has revealed that several categories of pottery were used for the preparation of foodstuffs. One particular type of beige residue has been identified on the inner surface of ceramic vessels from several sites. Chemical analyses of mineral residues, combined with the stylistic characteristics of ceramic vessels, have shown the consumption of bone powder. This consumption , far from being anecdotal, raises several questions regarding the diet behaviour of the earliest Neolithic communities in the Balkans, which have obviously sought a complementary source of calcium. Would the dietary transition at the beginning of the Neolithic period correspond to a diet stress?