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 curative conservation of this group of paintings requires specific actions leading to the chemical and physical stabilization of its constituent materials, diminishing its degradation. The works of curative conservation should be performed in the place where the paintings remain, the sacristy, in order to respect the already established seasoning of its materials, Casanovas (2006), reducing to maximum the risks of its deterioration due to RH and temperature oscillations, Casanovas (2006) .The action of the oxygen when strong oscillations of relative humidity act as an oxidant and hydrolyzant of layers containing water-soluble binding media, Matteini (1993) .Soluble components of paintings lost big mechanical properties and the effects of the solvents on paint must be tightly controlled, Mecklenburg (1998) .Since ground layers are made of organic binder with calcium sulphate (more anhydrite than gypsum) and organic binders have loss part of their properties due to the high RH they are exposed, aqueous and alkaline solvents must be avoided during the cleaning and overpaint removing phases, Mecklenburg (1998) . Aqueous fixatives can be used to return cohesiveness to the flaked ground layers, since its original materials have a good response when using this type of adhesives, as a combination of chemical attachment and mechanical union, Mecklenburg (1998). Although, these adhesives should be impregnated until the ground and sizing layers, activating the diffusion in all the directions of the flaking and taking advantage of the capillary effect of the ground layer, causing the adhesive to penetrate through the periphery of the lacunae and still leaving enough space for the air to escape in the lifted areas, re-placing it with cohesion, Nicolaus (1999) . Filling, retouching and protective materials used in the restoration of the lacunae of the wooden support, ground and painting layers must have a good resistance to high RH, considering the microclimatic changing conditions of the room. The aesthetic retouching must take into account the great percentage of loses of original painting. In order o achieve a compromise that respects global lecture of the set of paintings and not suggesting miss interpretations on aesthetic original intentions of the artist, it is imperious to discuss this matter in a multidisciplinary team, incorporating sciences such as conservation and restoration, art history, chemistry and physics. Conclusions The former altarpiece of Saint Catherine of Alexandria has been maintained at a high RH in the sacristy of Goa Cathedral for the last three centuries. The paintings reached a response to the RH fluctuations but not without damage.The damages occurred were related to important factors of ageing and materials reaction to high RH and its fluctuation: the expansion and contraction of the oak support, cracking and causing stress in the other materials of the painting; the loss of properties of organic binders, overall the hygroscopic glue, existing in sizing and ground layer, suffering a great expansion and contraction and responding with a low yield point to RH fluctuation. Overpainting is also a cause of deterioration of the original paintings. The better conservation of the three paintings restored in the last century when compared to the other five overpainted paintings, with significant loss of the original chromatic layer, puts in evidence the importance of the conservation and restoration, contributing to a better resistance and re-adaptation of the paintings to their environment. To conserve (preventive and curative), to restore the damaged paintings of this altarpiece and to keep this set of paintings equilibrated in its own environment is to promote its structural integrity and its preservation to future generations. 6. Acknowledgements The authors acknowledge to Most Rev. Filipe Neri Ferrão, Archbishop of Goa and Daman, to Fr. Joaquim Loiola Pereira and to Fr. Alfred Vas for allowing this study. Also wish to acknowledge to Fundação Calouste Gulbenkian for financial support trough the project “De artibus in auream Goa” and Fundação para a Ciência e Tecnologia for financial support (Post-doc grant SFRH/BPD/103315/2014). Also acknowledge Luís Dias and Sara Valadas for the assistance at the SEM-EDS, Stéphane Longelin for the assistance at the µ-Raman and Ana Cardoso for the assistance at the µ-FTIR. This work was supported by the research center grant no. UID/FIS/04559/2013 to LIBPhys-UNL, from the FCT/MCTES/PIDDAC and research center grant no. UID/Multi/04449/2013 to Hercules Laboratory. 5.