INDUCED BREAKDOWN SPECTROSCOPY; PIGMENTS

France is one of the countries involved in the future E-RIHS - European Research Infrastructure for Heritage Science. The research infrastructure dedicated to the study of materials of cultural and natural heritage will provide transnational access to state-of-the-art technologies (synchrotron, ion beams, lasers, portable methods, etc.) and scientific archives. E-RIHS addresses the experimental problems of knowledge and conservation of heritage materials (collections of art and natural museums, monuments, archaeological sites, archives, libraries, etc.). The cultural artefacts are characterized by complementary methods at multi-scales. The variety and the hybrid are specific of these artefacts and induce complex problems that are not expected in traditional Natural Science: paints, ceramics and glasses, metals, palaeontological specimens, lithic materials, graphic documents, etc. E-RIHS develops in that purpose transnational access to distributed platforms in many European countries. Five complementary accesses are in this way available: FIXLAB (access to fixed platforms for synchrotron, neutrons, ion beams, lasers, etc.), MOLAB (access to mobile examination and analytical methods to study the works in situ), ARCHLAB (access to scientific archives kept in the cultural institutions), DIGILAB (access to a digital infrastructure for the processing of quantitative data, implementing a policy on (re) use of data, choice of data formats, etc.) and finally EXPERTLAB (panels of experts for the implementation of collaborative and multidisciplinary projects for the study, the analysis and the conservation of heritage works). Thus E-RIHS is specifically involved in complex studies for the development of advanced high-resolution analytical and imaging tools. The privileged field of intervention of the infrastructure is that of the study of large corpora, collections and architectural ensembles. Based on previous I3 European program, and especially IPERION-CH program that support the creation of new mobile instrumentation, the French institutions are involved in the development of LIBS/LIF/RAMAN portable instrumentation. After a presentation of the challenge and the multiple advantages in building the European Infrastructure and of the French E-RIHS hub, the major interests of associating the three lasers based on analytical methods for a more global and precise characterization of the heritage objects taking into account their precious characters and their specific constraints. Lastly some preliminary results will be presented in order to give a first idea of the power of this analytical tool.

LIBS; prehistorical pigments; caves; calcite layer; climatic conditions;INDUCED BREAKDOWN SPECTROSCOPY

Painted caves are a specific environment which preservation needs multidisciplinary studies carried out within the different actors. The actions set-up must follow national and European ethics and treaties and be as less invasive as possible to preserve the integrity of the site. Studying colorants in caves should meet these expectations and take into account on-field conditions: high humidity rate, reduced access to electricity, etc. Therefore, non-invasive analyses should be preferred. However, their limits restrict the field of application and sometimes sampling and laboratory analyses must be used to answer the problematic. It is especially true when the pigment is covered by calcite. For this purpose, the Laser-Induced Breakdown Spectroscopy (LIBS) has been assessed to identify the composition with stratigraphic analyses. This study carries out in-depth profile on laboratory samples in conditions close to the ones meet in caves. Samples were prepared on a calcareous substrate using three pigments: red ochre, manganese black and carbon black and two binding media: water and saliva. All samples have been covered by calcite. Four sets of measurements have then been done using the LIBS instrument. The in-depth profiles were obtained using the Standard Normal Variate (SNV) normalization. For all the samples, the pigment layer was identified in the second or third shot, the calcite layer being quite thin. However, the results remain promising with the carbon black pigment but not really conclusive, the carbon being generally quite difficult to quantify.