The Use of Phosphonates to Inhibit Salt Crystallization: A Laboratory Study for the Sustainable Conservation of Mural Paintings in the Hypogea Context

Giulia Simonelli, Giancarlo Sidoti, Ludovica Ruggiero, Angela Calia, Giovanni Quarta, Fabio Aramini and Paola Mezzadri ()
Additional contact information
Giulia Simonelli: Independent Researcher, 00191 Rome, Italy
Giancarlo Sidoti: Istituto Centrale per il Restauro (ICR), Ministry of Culture, 00153 Rome, Italy
Ludovica Ruggiero: Ales Arte Lavoro e Servizi S.p.A., Istituto Centrale per il Restauro (ICR), Ministry of Culture, 00184 Rome, Italy
Angela Calia: Institute of Heritage Science, Italian National Council of Research (ISPC-CNR), 73100 Lecce, Italy
Giovanni Quarta: Institute of Heritage Science, Italian National Council of Research (ISPC-CNR), 73100 Lecce, Italy
Fabio Aramini: Istituto Centrale per il Restauro (ICR), Ministry of Culture, 00153 Rome, Italy
Paola Mezzadri: Istituto Centrale per il Restauro (ICR), Ministry of Culture, 00153 Rome, Italy

Sustainability, 2024, vol. 16, issue 22, 1-21

Abstract: This research is focused on the laboratory study of salt crystallization inhibitor products as new materials for conservation treatments which can be applied to mortars and painted plasters; as is well known, salt crystallization is one of the most frequent causes of decay processes on decorated architectural surfaces in a wide range of environments. Specifically, the study targets the field of the preventive conservation of mural paintings within rupestrian heritage sites. For the first time, systematic investigations were performed on mock-ups made of plaster painted with two different pigments: yellow ochre and carbon black. Two types of phosphonate inhibitors, PBTC (2-phosphonobutane-1,2,4-tricarboxylic acid) and ATMP (aminotris (methylene phosphonic acid)), were chosen and applied at two different concentrations. Given the limited literature available, and the presence of pigments potentially sensitive to treatment with salt inhibitors, preliminary tests were required. Their effects on the chromatic features of the pigments were evaluated visually and using colorimetry. The changes in the behaviour of water circulation in the mortar resulting from the treatments were evaluated through water vapour permeability and absorption tests. Accelerated crystallization experiments were carried out to assess how inhibitors could influence the growth of salts and the resulting material damage. The latter was carried out by employing sodium sulphate and calcium sulphate solutions, quantifying the damage to the specimens through material loss in weight and the percentage of painted surface loss. Based on the overall results, the product with the best performance was identified was ATMP 0.1% (by volume) in deionized water. The obtained results show that salt inhibitor treatments are promising for in situ application and could represent an innovative approach to promote the sustainable conservation of mural painting, particularly those located in hypogeal contexts, where the salt supply cannot be removed and slowing the growth of salts and/or changing their crystalline habitus may be effective in limiting their damage.

Keywords: hypogea; mural painting; crystallization inhibitors; salt damage (search for similar items in EconPapers)
JEL-codes: O13 Q Q0 Q2 Q3 Q5 Q56 (search for similar items in EconPapers)
Date: 2024
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