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International audience; In recent years, we have seen a significant increase in interest in the effects of irradiation used for analytical purposes on art, archaeological, palaeontological and palaeoenvironmental samples and objects. Among the main trends regarding ionising radiations used in X-ray, UV and ion beam experiments, we have observed a greater consistency in the description of the effects of irradiation, a number of quantitative studies, while several works studied in depth the corresponding chemical mechanisms and kinetics. We have also observed the development of analytical strategies and dedicated instruments to better detect and limit the effects of irradiation in real experiments on ancient samples and objects. Emerging trends include detailed mechanistic studies on specific systems, the development of statistical methods to reduce the doses required to study samples, and the development of early warning systems capable of feeding back into the experiment while an acquisition is in progress.

International audience; Egyptian blue and green are among the oldest synthetic pigments produced by humanity. The two pigments are complex multi-phase copper-based systems synthesised with different protocols from the same raw materials. Since the 2000s, synchrotron X-ray techniques have provided significant new insights on their chemistry and microstructure. However, the potential impact of high flux irradiation of these pigments has not yet been studied despite the fact that it can lead to visual discoloration and less readily observable alterations such as defects formation or redox changes. In this work, we investigate the effects of synchrotron X-ray irradiation on Egyptian blue and green samples. Radiation-induced effects are monitored after irradiation at increasing doses using electron paramagnetic resonance (EPR) spectroscopy at temperatures of 290 K and 30 K. The cupric ion (Cu2+) is in D4h axial geometry in Egyptian blue and in disordered geometry in Egyptian green, which makes the two pigments very easily identifiable by EPR. Egyptian green samples are found to be much more sensitive to X-rays than Egyptian blue. In particular, a browning of the green samples is observed from the lowest doses tested while no color change is detected for the blue ones. Three types of radiation-induced defects are detected after irradiation: E′, non-bonding oxygen hole and aluminum hole centers. Correlations between defect intensity and dose are calculated. Archaeological and modern pigments (whether blue or green) do not show the same reactivity to X-rays, which opens the prospect of using radiation-induced defects as a marker of their history.

International audience; X-ray analytical techniques are increasingly being used to study manuscripts and works of art on paper, whether with laboratory equipment or synchrotron sources. However, it is difficult to anticipate the impact of X-ray photons on paper- and cellulose-based artifacts, particularly due to the large variety of their constituents and degradation levels, and the subsequent material multiscale heterogeneity. In this context, this work aims at developing an analytical approach to study the modifications in paper upon synchrotron radiation (SR) X-ray radiation using analytical techniques, which are fully complementary and highly sensitive, yet not frequently used together. At the molecular scale, cellulose chain scissions and hydroxyl free radicals were measured using chromatographic separation techniques (size-exclusion chromatography-multiangle laser light scattering-differential refractive index (SEC-MALS-DRI) and reversed-phase high-performance liquid chromatography-fluorescence detector-diode array detector (RP-HPLC-FLD-DAD)), while the optical properties of paper were characterized using spectroscopy (UV luminescence and diffuse reflectance). These techniques showed different sensitivities toward the detection of changes. The modifications in the cellulosic material were monitored in real time, within a few days, and up to 2 years following the irradiation to define a lowest observed adverse effect dose (LOAED). As paper is a hygroscopic material, the impact of the humidity in the environment was studied using this approach. Three levels of moisture content in the paper, achieved by conditioning the samples and irradiating them at different relative humidities (RHs), were studied (0, 50, 80% RH). It was shown that very low moisture content accelerated molecular and optical modification