https://doi.org/10.1140/epjp/s13360-023-04069-z
Regular Article
Treating gypsum plaster cast artifacts by fillers: chemical and mechanical evaluation
1
Héritages : Culture(S), Patrimoine(S), Création(S), UMR 9022, CYU, CNRS, Ministère de la Culture, CY Cergy Paris Université, 33 Boulevard du Port, 95011, Cergy, France
2
LRMH – CRC UAR 3224 CNRS, Laboratoire de Recherche des Monuments Historiques, 29 rue de Paris, 77420, Champs-sur-Marne, France
3
Centre National de la Recherche Scientifique, Ministère de la Culture, UMR171 et UMR8247 MIN CULTURE, PSL Research University, Chimie ParisTech – CNRS, Institut de Recherche de Chimie Paris, Centre de Recherche et de Restauration des Musées de France, Palais du Louvre 14 Quai François Mitterand, 75001, Paris, France
4
Département des Restaurateurs, Institut National du Patrimoine, 2, rue Vivienne, 75002, Paris, France
5
Ministère de la Culture, 182 rue Saint-Honoré, 75001, Paris, France
6
Musée du Louvre, 75058, Paris Cedex 01, France
a
juliette.robin-dupire@culture.gouv.fr
Received:
15
October
2022
Accepted:
6
May
2023
Published online:
7
June
2023
Gypsum plaster cast artifacts frequently present losses that have to be filled to regain structural stability and satisfactory aesthetic, following deontological criteria such as stability, legibility, or non-damaging treatment. A multidisciplinary methodology was developed to assess filling methods and materials. Common fillers were selected and analysed, including gypsum plaster at different water/plaster mass ratios (W/P) and additives such as calcium carbonate and titanium dioxide. Multiscale structural visualisations and analyses, by optical microscopy and scanning electron microscopy with energy-dispersive X-ray spectroscopy, confirmed the elemental composition of the formulations and showed the differences in structure, crystallisation state, and porosity. Shear stress and consistency estimations, by a rheological study with plane–plane and Vane geometries, revealed shear thinning and visco-plastic behaviours and permitted to range textures from modelling paste to casting fluid. Quantification of mechanical properties at solid state, by resonance frequency measurements, flexural and compressive tests, pointed out a functional link between ultimate strength, E modulus, water proportion, and density of the formulations. Fillings behaviours were evaluated by high-definition 3D scanning and images correlation of three artifacts, presenting good stability or slow inertia. Increasing the proportion of water tends to loosen the structure and to add more pores, to liquefy the texture, and to lower the ultimate strength. With crystals filling the porosity of gypsum plaster, additives tend to thicken the fluid texture and to increase the ultimate strength. Those quantifications of formulations can help professional to choose fitted material, according to the specifics of each filling treatment.
© The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2023. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
