Abstract
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.
Highlights
The present paper aimed at investigating the effectiveness and the compatibility of two treatments that have been taken into consideration for the conservation of prehistoric paintings in the Magura cave
The Magura cave limestone was found to be mainly composed of calcite, quantified as 90.0 ± 1.8 wt.%
After treatment with “diammonium hydrogen phosphate (DAP)”, clusters ofclusters the new of calcium phosphates phosphates the stone surface, alsowas in this was not continuously coated were visible were on thevisible stone on surface, which, inwhich, this case, notcase, continuously coated with the new with the Generally, new phases.new
Summary
The present paper aimed at investigating the effectiveness and the compatibility of two treatments that have been taken into consideration for the conservation of prehistoric paintings in the Magura cave (northwest Bulgaria). The Magura cave contains impressive prehistoric paintings, displaying both figurative and abstract compositions [1]. Religious ceremonies, hunting scenes, signs, and graphic motifs decorate one of the cave chambers—the Gallery with the paintings (Figure 1). Coatings 2020, 10, x FOR PEER REVIEW Figure.
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