PSI - Issue 5

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

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variations effects on the studied paintings are associated to the response of the ground and to paint layers. It must be considered that measures were taken in winter period, with oscillations from 26 to 28,5 in the 5 days measured (Table1), most probably increasing over 30ºC for the summer period. When a painting is illuminated, the entire range of radiation is absorbed by the materials of which the painting is composed and degrade the molecular structure and macroscopic properties of these materials, mostly of organic origin Herráez (2014), . Illuminance had an oscillation from 3 to 114 Lux during the measuring period (Table1). Table 1.Temperature (ºC), relative humidity (%) and lux measures for five days of months of January/February in sacristy of Goa Cathedral. Day Hour (h) Temperature (°C) Relative Humidity (%) Illuminance (Lux) 30-1-2017 10 26,3 79 15-19 30-1-2017 11 26 81 15-30 30-1-2017 15 26,4 69 69-81 30-1-2017 19 26,9 71 10-15 31-1-2017 11 26,8 70 25-32 31-1-2017 15 27 76 40-114 3-2-2017 19 26,8 74 2-5 4-2-2017 15 28,5 68 25-30 4-2-2017 19 27 71 22-27 4-2-2017 20 27 79 3-6 6-2-2017 10 27 75 14-17 The wooden support, if restrained during changes in relative humidity respond by swelling and shrinking with high stress and strains. It is possible to verify cracks in some boards due to its movements caused by mechanical strengths due to RH oscillations and biologic attack, Mecklenburg (1998) (Figures1a and 1b). These responses bring also stress to the painting layers. a b

Fig. 1. (a) “Saint Catherine of Alexandria with martyr's palm”, oil on oak panel painting, made circa 1540, assigned to Portuguese painter Garcia Fernandes, belonging to the former altarpiece and nowadays in Goa Cathedral Sacristy; (b) cracks in board and chromatic layer of the same painting, caused by mechanical strengths due to RH oscillations and biologic degradation. The most common deterioration found in the majority of the damaged paintings is layer separation, for the detachment of ground layer from the support causing the paint to flake. In some parts of the most degraded paintings is possible to find lifting ground layers on the topography of these paintings, under an examination by raking light (Figures 2a and 2b), Stoner (2012) . a b

Fig. 2. (a) Lifting ground layers, under an examination by raking light; (b) detachment and lifting ground layers, under an examination by raking light.