Unravelling materials, provenance, and serial manufacturing of the «Madonne di gesso» : A first technical study on stucco devotional reliefs from Italian Renaissance Masters

Dans l’Italie de la Renaissance ont été largement diffusées des séries de reliefs en «stuc», souvent représentant la Vierge etl’Enfant, créées à partir des modèles de grands sculpteurs de l’époque. Malgré leur présence très abondante dans les collectionsde musées, très peu d’études d’envergure ont été entreprises sur le matériau constitutif. Dans cette thèse, intégrée dans le projetESPRIT, grâce à la mise en oeuvre d’un protocole analytique multiple permettant la caractérisation multi-échelle du stuc, trois axesde recherche ont été explorés : l’identification du matériau et des témoins de leur mise en oeuvre, l’origine des matières premièreset l’étude de la sérialité des productionsLes analyses par XRD, SEM-EDX et PIXE révèlent que les 30 reliefs du corpus sont constitués de stucs gypseux, contenant 40-44wt% CaO pour 52-56 wt% SO3. Les mesures par PIXE et LA-ICP MS des éléments traces d’une part et l’étude de la forme des poreset l’estimation du taux de gâchage par SR-μCT d’autre part permettent de mettre en évidence un ensemble de plus de 20 oeuvresprésentant les mêmes caractéristiques. Cette constatation confirmerait l’hypothèse d’une zone de production majeure, peut-êtreFlorence selon les historiens d’art. Des variations légères dans les proportions d’éléments traces, dans le taux de gâchage ouencore dans les microstructures peuvent être des indices d’ateliers différents, mais toujours autour de Florence. L’analyseminéralogique et géochimique ou isotopique d’une trentaine d’échantillons de matériaux gypseux provenant de 3 carrières degypse et d’albâtre proches de Florence montre que les carrières miocènes seraient peut-être les sources d’approvisionnement enmatière première.Des proportions différentes de minéraux accessoires, notamment des argiles plus ou moins riches en Potassium et Magnésium,ainsi que des teneurs différentes en éléments traces dont des terres rares, des mésopores de formes différentes, indices d’unegranulométrie différente de la matière première utilisée ont été détectés dans quelques oeuvres. Créées d’après des modèles parDonatello (et Bellano) et Rossellino, deux artistes ayant résidé dans plusieurs régions d’Italie, ces oeuvres ont peut-être étéréalisées dans d’autres lieux que l’espace florentin, comme le nord de l’Italie.En parallèle, des tests ont été réalisés par THz-TDI et par radiographie X/tomographie, pour tenter de mettre en évidence demanière non destructive la stratigraphie des différentes couches de plâtre, témoin de la mise en oeuvre des matériaux lors dumoulageEnfin, l’aspect sériel des productions a été abordé à travers l’analyse par scan 3D, de 3 séries de tirages appartenant à 3 modèlesd’après Donatello, Desidério da Settignano et Rossellino. Les données obtenues permettent de comparer et de quantifier lessimilitudes et les différences d’un tirage à l’autre et de proposer ensuite une chronologie dans les tirages et de vérifierl’appartenance de chaque pièce à une même génération de moulages.The production of devotional reliefs flourished in 15th century Florence, where original marble models from Renaissance Masters were moulded to be reproduced in series. Among the materials mostly used to this purpose was the so-called “stucco”. Despite the wide diffusion of stucco reliefs, details concerning their constitutive materials and manufacturing processes are fragmentary and poorly studied. In the framework of a multidisciplinary project fostered by the Louvre Museum, this thesis explored three research lines in order to: 1) identify and characterise stucco mineral constituents; 2) determine raw material provenance; 3) investigate manufacturing techniques and serial casting processes.A multi-analytical approach was devised to investigate composition (SEM-EDX, PIXE, LA-ICP-MS) and structure (XRD, FEG-SEM, SµCT) of micro samples obtained from 30 representative artworks attributed to 7 Florentine Masters.Results showed that all the artworks are made of a gypsum based stucco (40-44 wt% CaO and 52-56 wt% SO3) with secondary mineral phases (anhydrite, calcite, dolomite, celestine and clay minerals) in few weight percentage maximum.PIXE and LA-ICP MS trace elements analyses, the study of W/P ratio and pores morphology by SEM-EDX and SµCT, pointed out that about 20 reliefs present similar compositional and structural parameters. This confirms the hypothesis of common practices and of a common production centre according to the Florentine attribution of the artworks.A geological survey was performed in 3 quarries in the surroundings of Florence and the provenance of the raw gypsum was investigated by means of geochemical and isotopic composition. In particular synsedimentary clay minerals with variable amounts of K, Mg and Fe, related trace elements (e.g. Ti and REE), and multi isotopic fingerprint (S, O, Sr) have been tested as provenance markers. Usefulness and pitfalls of the approach were verified through a first promising comparison with data obtained on stucco reliefs. Miocene quarries seems to have compatible signature with the ones measured on artworks.Nonetheless, small differences related both to accessory minerals proportions, to trace element contents, and to pores microstructures suggest that some of the stucco reliefs after models of Donatello and A. Rossellino might have been produced following different practices or particularly by using different raw materials. These evidences, corroborated by the activity of these artists in many Italian regions, raise the hypothesis of the production of these casts outside the Florentine area.In parallel, THz-TDI, Xray radiography and Computed Tomography were tested for the non-invasive investigation of the internal stratigraphy of plaster layers possibly revealing different manufacturing techniques.Finally, serial manufacturing techniques were investigated on 3 groups of replicas belonging to 3 models after Donatello & B. Bellano, D. da Settignano and A. Rossellino. Structured light 3D scanner and mesh comparison of the 3D models obtained on stucco casts proved to be a very useful tool. The method allowed to measure millimetric differences of shapes and topography among reliefs stored at the Louvre, Bargello and Bardini Museum. This helped to find direct correlations between casts, to verify which ones were most likely produced with the same mould, and to propose a chronology within the same casting series.Results obtained disclosed new and important insights on the practices of 15th century Florentine botteghe and on the manufacturing of these artworks. This work and the large set of data produced will also provide solid basis for further investigations and will hopefully prompt interest on this topic worth to be studied with increased attention

Microstructure imaging of Florentine stuccoes through X-ray tomography: A new insight on ancient plaster-making techniques

International audienceGypsum-based plasters or stuccoes, in spite of their importance and diffusion, received little attention in cultural heritage materials studies. This work introduces a new, non-destructive methodology, using micro-tomography to measure the water/plaster ratio and the morphology of the hemihydrate powder used to make plasters on < 1 mm3 samples. This methodology give insight in both the raw material (and ultimately provenance) and the technique used to make plaster. The methodology was tested first on mock-up samples of known composition, then in a case study on 13 low-relief cast plaster sculptures from 15th century Florentine artists. Preliminary conclusions on this limited corpus show relative uniformity across most reliefs in terms of raw materials and techniques. The casts of one model (Nativity, attributed to Donatello and B. Bellano) were made with a different raw material, in line with prior geochemical analyses; these results support the previous attribution to a North Italian rather than Florentine origin. The casts of a second model (Virgin and Child, type of Saint Petersburg, attributed to Antonio Rossellino) were prepared with a different technique. This surprising result was not expected from Art History or previous studies

Synchrotron radiation soft X-ray microscopy and low energy X-ray fluorescence to reveal elemental changes in spermatozoa treated with photobiomodulation therapy

Male infertility is a worldwide clinical issue that increases the number of couples resorting to assisted reproductive technologies (ARTs) to achieve pregnancy. Photobiomodulation therapy (PBMT) is a promising technique that can biostimulate cells and tissues and it is currently successfully employed to enhance the sperm motility in vitro. Nevertheless, its use has been so far restricted to the research field. In the present work, we exploited two PBMT protocols at an 800 nm wavelength on sperm derived from infertile individuals, detecting an increase in sperm motility 1 hour after irradiation. Moreover, in order to add new information about the molecular effect of PBMT, the content of some light elements was evaluated using high resolution X-ray fluorescence imaging. Interestingly, an increase in Na content was detected in the irradiated samples, possibly suggesting a role of this element in sperm motility; indeed, a low Na content was previously correlated with a poor sperm quality, low semen volume, and modest fertilization rate. Amplifying the knowledge of PBMT in the ART field will expedite the translational potentiality of the PBMT use in clinical settings

Synchrotron Radiation Study of Gain, Noise, and Collection Efficiency of GaAs SAM-APDs with Staircase Structure

In hard X-ray applications that require high detection efficiency and short response times, such as synchrotron radiation-based Mössbauer absorption spectroscopy and time-resolved fluorescence or photon beam position monitoring, III–V-compound semiconductors, and dedicated alloys offer some advantages over the Si-based technologies traditionally used in solid-state photodetectors. Amongst them, gallium arsenide (GaAs) is one of the most valuable materials thanks to its unique characteristics. At the same time, implementing charge-multiplication mechanisms within the sensor may become of critical importance in cases where the photogenerated signal needs an intrinsic amplification before being acquired by the front-end electronics, such as in the case of a very weak photon flux or when single-photon detection is required. Some GaAs-based avalanche photodiodes (APDs) were grown by a molecular beam epitaxy to fulfill these needs; by means of band gap engineering, we realised devices with separate absorption and multiplication region(s) (SAM), the latter featuring a so-called staircase structure to reduce the multiplication noise. This work reports on the experimental characterisations of gain, noise, and charge collection efficiencies of three series of GaAs APDs featuring different thicknesses of the absorption regions. These devices have been developed to investigate the role of such thicknesses and the presence of traps or defects at the metal–semiconductor interfaces responsible for charge loss, in order to lay the groundwork for the future development of very thick GaAs devices (thicker than 100 [Formula: see text] m) for hard X-rays. Several measurements were carried out on such devices with both lasers and synchrotron light sources, inducing photon absorption with X-ray microbeams at variable and controlled depths. In this way, we verified both the role of the thickness of the absorption region in the collection efficiency and the possibility of using the APDs without reaching the punch-through voltage, thus preventing the noise induced by charge multiplication in the absorption region. These devices, with thicknesses suitable for soft X-ray detection, have also shown good characteristics in terms of internal amplification and reduction of multiplication noise, in line with numerical simulations

Impact of Sample Preparation Methods on Single-Cell X-ray Microscopy and Light Elemental Analysis Evaluated by Combined Low Energy X-ray Fluorescence, STXM and AFM

BACKGROUND: Although X-ray fluorescence microscopy is becoming a widely used technique for single-cell analysis, sample preparation for this microscopy remains one of the main challenges in obtaining optimal conditions for the measurements in the X-ray regime. The information available to researchers on sample treatment is inadequate and unclear, sometimes leading to wasted time and jeopardizing the experiment's success. Many cell fixation methods have been described, but none of them have been systematically tested and declared the most suitable for synchrotron X-ray microscopy. METHODS: The HEC-1-A endometrial cells, human spermatozoa, and human embryonic kidney (HEK-293) cells were fixed with organic solvents and cross-linking methods: 70% ethanol, 3.7%, and 2% paraformaldehyde; in addition, HEK-293 cells were subjected to methanol/ C3H6O treatment and cryofixation. Fixation methods were compared by coupling low-energy X-ray fluorescence with scanning transmission X-ray microscopy and atomic force microscopy. RESULTS: Organic solvents lead to greater dehydration of cells, which has the most significant effect on the distribution and depletion of diffusion elements. Paraformaldehyde provides robust and reproducible data. Finally, the cryofixed cells provide the best morphology and element content results. CONCLUSION: Although cryofixation seems to be the most appropriate method as it allows for keeping cells closer to physiological conditions, it has some technical limitations. Paraformaldehyde, when used at the average concentration of 3.7%, is also an excellent alternative for X-ray microscopy.This research was partially supported by the Italian Ministry of Health, through the contribution given to the Institute for Maternal and Child Health IRCCS Burlo Garofolo Trieste, Italy (5mille15D1; 5xmille SD03/22). Part of this work has been performed in the frame of the INTEGRA CERIC-ERIC research project

Impact of Sample Preparation Methods on Single-Cell X-ray Microscopy and Light Elemental Analysis Evaluated by Combined Low Energy X-ray Fluorescence, STXM and AFM

Background: Although X-ray fluorescence microscopy is becoming a widely used technique for single-cell analysis, sample preparation for this microscopy remains one of the main challenges in obtaining optimal conditions for the measurements in the X-ray regime. The information available to researchers on sample treatment is inadequate and unclear, sometimes leading to wasted time and jeopardizing the experiment’s success. Many cell fixation methods have been described, but none of them have been systematically tested and declared the most suitable for synchrotron X-ray microscopy. Methods: The HEC-1-A endometrial cells, human spermatozoa, and human embryonic kidney (HEK-293) cells were fixed with organic solvents and cross-linking methods: 70% ethanol, 3.7%, and 2% paraformaldehyde; in addition, HEK-293 cells were subjected to methanol/ C3H6O treatment and cryofixation. Fixation methods were compared by coupling low-energy X-ray fluorescence with scanning transmission X-ray microscopy and atomic force microscopy. Results: Organic solvents lead to greater dehydration of cells, which has the most significant effect on the distribution and depletion of diffusion elements. Paraformaldehyde provides robust and reproducible data. Finally, the cryofixed cells provide the best morphology and element content results. Conclusion: Although cryofixation seems to be the most appropriate method as it allows for keeping cells closer to physiological conditions, it has some technical limitations. Paraformaldehyde, when used at the average concentration of 3.7%, is also an excellent alternative for X-ray microscopy

Protocol for lapis lazuli provenance determination: evidence for an Afghan origin of the stones used for ancient carved artefacts kept at the Egyptian Museum of Florence (Italy)

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