Centre d'Analyses et de Recherche en Art et ArchéologieThe analytical techniques used at CARAA in collaboration with associated laboratories and universities make use of bench and mobile instruments.
They includes :
• Environmental scanning electron microscopy coupled with Energy dispersive spectroscopy (ESEM-EDS):
Energy dispersion spectrometer (EDS) provides the elemental composition of pigments in a painting (e.g. Fe for iron oxides, Hg for cinnabar, As for realgar, Cu for azurite, etc..) or helps to determine the chemical content of the different chemical elements (e.g Si, Ca, K, Na, Mg, Fe, etc. in siliceous-based objects). The scanning electron microscopy (SEM) allows, among others to view high-magnification morphology and arrangement of crystals and fibers in a sample.
• Portable X-ray fluorescence spectroscopy (XRF) :
Portable X-ray fluorescence device (XRF) allows to determine the exact composition of e.g. an alloy without making any sampling. It provides the elemental composition of pigments in a painting (e.g. Fe for iron oxides, Hg for cinnabar or vermilion, As for realgar, Cu for azurite, etc..) or the content of light and metallic elements (e.g. Si, Ca, K, Mg, Fe, Cu, etc..) in siliceous objects. XRF is also a perfect tool to detect toxic inorganic elements such as lead, arsenic or mercury.
• Electron microprobe (EMPA) :
Electron microprobe as EDS (energy dispersive spectrometer), can perform extensive quantitative analysis. These techniques allow for example to characterize the composition of a metal alloy and therefore to assess the adequacy of this alloy and its alteration with the attributed date of the object.
• Inductively coupled plasma mass spectroscopy (ICP-MS) :
CP-MS is a thorough analytical technique that provides ppm (parts-per-million) concentrations that allows for example to determine the trace elements concentration in an objects (eg, vanadium (V), thorium (Th), lead (Pb), etc.. in glasses or ceramics). These elements can often help to determine the geographic source of raw materials used for the manufacturing.
• Nano-SIMS
• Raman microscopy :
Raman microscopy is a molecular and mineralogical technique that is very efficient for the characterization of metallic alteration products, dies, pigments or siliceous material. Raman microscopy or X-ray diffraction (DX) are often complementary to XRF and allow to obtain the molecular or mineral composition of pigments (e.g., hematite-Fe2O3, cinnabar-HgS-,-realgar As4S4-, malachite -Cu2(CO3)(OH)2). However, unlike X-ray diffraction, Raman microscopy also permit the analysis of organic (such as polymers or plastics) or amorphous materials (such as coal or graphite).
• X-ray diffraction (XRD) :
When elemental analysis such as X-ray fluorescence allows to determine what, and in which proportions, are present the atoms in a sample, X-ray diffraction permits to know the organization of the matter. It allows for example, to distinguish the different alumina (aluminum oxide) although they all have exactly the same elemental composition. Furthermore, X-ray diffraction on crystalline material provides access to physical information on the crystals, including their size and orientation.
However, this technique can only be used on crystalline material, ie mainly rocks, metals, ceramics, and some organics.
• Fourier transform infrared spectroscopy (FTIR) :
Fourier Transform Infrared Spectroscopy is based on the absorption of infrared radiation by the material being analyzed. It enables, through the detection of characteristic vibrations of the chemical bonds, to carry out the analysis of the chemical functions present in the material.
This technique is simple and not destructive. It allows the analysis of both organic and inorganic materials. From an FTIR spectrum, it is possible to identify the nature of a natural organic material or of synthetic ones, their oxidation state, the presence of mineral fillers and of a large number of colored pigments. It is mainly used in the field of Arts to characterize organic substances: binders, genuine materials or added during later restorations.
• Liquid and gas chromatography coupled with masse spectroscopy (HPLC & GC-MS) :
Gas chromatography (GC) or liquid chromatography (HPLC) are, like all chromatographic techniques used to separate very complex and very diverse molecules from an organic mixture. They are therefore perfectly adapted to the analysis of the composition of many modern or ancient objects from the cultural heritage field (e.g. waxes, resins, gums, tannins, oils, etc.).
When mixtures are too complex or with a very high polarity, HPLC is then preferred to GC. It is used particularly in the analysis of the pigments, dyes, tannins or old resins.
