PSI - Issue 5

Vanessa Antunes et al. / Procedia Structural Integrity 5 (2017) 1078–1085 Vanessa Antunes/ Structural Integrity Procedia 00 (2017) 000 – 000

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The increase of RH and small vibrations in the painting may lead to the fall of these degraded areas, overall in what concerns to water-based binding media, Nicolaus (1999) such as the ground layers, probably originally made with a mixture of calcium sulphate and animal glue, as stated in treatises of that period, Nunes (1982) . EDS analysis confirmed the ground layer as being a C, S matrix (Figure 3a). Micro-XRD analysis indicate that the studied ground layers are a mixture of calcium sulphates, with anhydrite and a small amount of gypsum (Figure 3b),similar to other results already obtained for the Lisbon workshop, Antunes (2014a) (2014b) . a b

Fig. 3. (a)EDS analysis confirmed the ground as being a C, S matrix; (b) Micro-XRD analysis of ground layers showing anhydrite area of peaks at 3,50 Å and a small amount of gypsum, area of peaks at 3,06 Å. Raman analysis confirmed the presence of anhydrite. Results brought by the µ-FTIR analysis (Figure 4a) specify the presence in the ground layer of oil and small amount of proteic material, being probably animal glue. Py-GC/MS with derivatisation confirmed the use of linseed oil. However it was not possible at this time to confirm the presence of animal glue (Figure 4b). a b

Fig. 4. (a)Micro-FTIR analysis indicates the presence in the ground layer of small quantity of proteins, of of fatty acids of oil, anhidrite, gypsum and silicates; (b) Pyrogram of ground layer, in the presence of TMAH derivatization reagent, suggesting the presence of linseed oil as binder. Peak identification as Palmitic acid, Stearic acid, TMAH pyrolysis products. This result was based in the variation between palmitic and stearic acids, Bonaduce (2009) .The undetection of proteic binder in the ground layer by Py-GC/MS, may indicate that the proteic binder could have been used in small quantity and/or, most probably, can be degraded due to the high RH conditions and oscillations of the paintings environment. The contact with the air, the light, pollutants and humidity can change the composition of a pigment, a binder or a