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Open AccessFeature PaperArticle

Comparative Study Between Ammonium Phosphate and Ethyl Silicate Towards Conservation of Prehistoric Paintings in the Magura Cave (Bulgaria)

1
Department of Civil, Chemical, Environmental and Materials Engineering (DICAM), University of Bologna, Via Terracini 28, 40131 Bologna, Italy
2
Centre for Applied Research on Buildings and Construction (CIRI-EC), University of Bologna, Via del Lazzaretto 15/5, 40131 Bologna, Italy
3
NTConservation ltd, Blv. Al. Konstantinov 51, 1504 Sofia, Bulgaria
4
Nadir srl Plasma & Polymers, Via Torino 155/b, 30172 Venezia, Italy
*
Author to whom correspondence should be addressed.
Coatings 2020, 10(3), 250; https://doi.org/10.3390/coatings10030250
Received: 16 January 2020 / Revised: 5 March 2020 / Accepted: 6 March 2020 / Published: 9 March 2020
(This article belongs to the Special Issue Ion-Substituted Calcium Phosphates Coatings)
This study aimed at evaluating the effectiveness and the compatibility of two alternative treatments, in view of their possible use for conservation of prehistoric paintings in the Magura cave (Bulgaria). The paintings are made of bat guano applied over limestone; therefore, two sets of laboratory specimens were considered: stone specimens and stone specimens covered with a layer of sterilized bat guano. The two investigated treatments were a commercial product based on ethyl silicate (“ES”) and a solution of diammonium hydrogen phosphate (“DAP”), aimed at forming calcium phosphates. The results of the study indicated that both treatments were able to increase the mechanical properties of stone, the increase being higher for “DAP”. Both consolidants caused acceptable color changes, but the “ES” treatment significantly decreased stone wettability, water absorption, and water vapor permeability, while the “DAP” treatment slightly affected those properties. In the stone + guano specimens, the presence of the guano layer affected the penetration of the consolidants, thus partly reducing their effectiveness. Compared to the stone samples, the guano layer experienced a more intense color change, alongside visible cracking. However, the adopted methodology to replicate the cave paintings was not completely successful, as the so-deposited guano layer was very prone to detachment when dry, unlike cave paintings. Future work will be dedicated to assessing the consolidant performance onto samples that resemble even more closely the conditions of the cave paintings, by improving the methodology for the guano layer deposition and by contaminating specimens with soluble salts before consolidant application. View Full-Text
Keywords: cave painting; inorganic consolidant; hydroxyapatite; calcium phosphate; ammonium phosphate; ethyl silicate; TEOS; non-thermal plasma; wettability cave painting; inorganic consolidant; hydroxyapatite; calcium phosphate; ammonium phosphate; ethyl silicate; TEOS; non-thermal plasma; wettability
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MDPI and ACS Style

Sassoni, E.; Franzoni, E.; Stefanova, M.; Kamenarov, Z.; Scopece, P.; Verga Falzacappa, E. Comparative Study Between Ammonium Phosphate and Ethyl Silicate Towards Conservation of Prehistoric Paintings in the Magura Cave (Bulgaria). Coatings 2020, 10, 250.

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