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Article

New Insights into the Geochemical Processes Occurring on the Surface of Stuccoes Made of Slaked Lime Putty

1
Independent Researcher, 08450 Llinars del Vallès, Spain
2
Departament d’Arts i Conservació-Restauració, Facultat de Belles Arts, Universitat de Barcelona, c/Pau Gargallo 4, 08028 Barcelona, Spain
3
Institut d’Arqueologia de la Universitat de Barcelona, c/Montalegre 6-8, 08001 Barcelona, Spain
4
Institut Universitari de Restauració del Patrimoni, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain
5
Escola Superior de Conservació i Restauració de Béns Culturals de Catalunya, c/ d’Aiguablava, 109-113, 08033 Barcelona, Spain
*
Author to whom correspondence should be addressed.
Crystals 2023, 13(2), 219; https://doi.org/10.3390/cryst13020219
Received: 14 December 2022 / Revised: 18 January 2023 / Accepted: 20 January 2023 / Published: 24 January 2023
(This article belongs to the Special Issue Archaeological Crystalline Materials)

Abstract

The fresco technique performed with slaked lime putty as binding material has been well known since Antiquity. However, the geochemical processes that occur on the surface have been generally described as part of the carbonation process of the intonaco itself. When approaching this technique from experimental archaeology, it has been observed for the first time that during the execution period (from 0 to 20 h, approximately) the processes occurring on the surface of the stucco are different from those occurring inside. Furthermore, these processes lead to the formation of an epigenetic film of specific texture, stiffness and compactness. This study investigates the formation and evolution of this surface film using a series of slaked lime putty stucco test tubes. Samples were extracted at different intervals and subsequently analyzed by polarized optical microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. Results indicate that the development of the film, composed of an amorphous gel-like stratum and a micro-crystalline stratum, occurs in parallel to the carbonation occurring inside the stucco. Moreover, this process does not respond to the classical geological processes of calcium carbonate formation. It was also observed that its presence slows down the carbonation in the underlying strata (intonaco, intonachino, arriccio, etc.) and that the surface becomes more crystalline over time. The identification of this film has implications for the field of the conservation–restoration of fresco paintings and lime-based wall paintings.
Keywords: fresco technique; stucco; carbonation process; epigenetic film; POM; SEM; FTIR fresco technique; stucco; carbonation process; epigenetic film; POM; SEM; FTIR

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MDPI and ACS Style

Pocostales, L.; Pitarch Martí, À.; Guasch-Ferré, N.; Doménech-Carbó, M.T.; Prada Pérez, J.L. New Insights into the Geochemical Processes Occurring on the Surface of Stuccoes Made of Slaked Lime Putty. Crystals 2023, 13, 219. https://doi.org/10.3390/cryst13020219

AMA Style

Pocostales L, Pitarch Martí À, Guasch-Ferré N, Doménech-Carbó MT, Prada Pérez JL. New Insights into the Geochemical Processes Occurring on the Surface of Stuccoes Made of Slaked Lime Putty. Crystals. 2023; 13(2):219. https://doi.org/10.3390/cryst13020219

Chicago/Turabian Style

Pocostales, Luciana, Àfrica Pitarch Martí, Núria Guasch-Ferré, María Teresa Doménech-Carbó, and José Luís Prada Pérez. 2023. "New Insights into the Geochemical Processes Occurring on the Surface of Stuccoes Made of Slaked Lime Putty" Crystals 13, no. 2: 219. https://doi.org/10.3390/cryst13020219

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