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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layer, Matteini (1993) . It can be considered that part of the water-based binding media of the ground layer were disintegrated with aging and by biological, chemical and physical reactions, decreasing the adhesion between pigment and binder, Nicolaus (1999) .These reactions had soften the ground and lead to a loss of cohesion of this layer, Nicolaus (1999), Matteini (1993) , visible by naked eye in several parts of the paintings. Swelling and cracking due to aging and hygroscopicity to thermo-hygrometric changes are visible too in the grid cracks covering all the pictorial surface and ground layer (Figure 5a). The direct contact with high RH promoted the blanching of the chromatic surface and varnish by the loss of contact between pigment and binding media, Nicolaus (1999) (Figure 5b). a b

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Fig. 5. (a)Grid cracks covering all the pictorial surface and ground layer showing primary and secondary fissures; (b) direct contact with high RH promoted the blanching of the chromatic surface and varnish. Sizing animal glue layer, placed between the wooden support and the ground layer, Nunes (1982), Antunes (2014c), has been studied as one of the most dimensionally receptive to humidity changes, Mecklenburg (1998) . Animal glue over a wood panel swell or shrinks in a RH range of 35% to 60% and at circa 68% the swelling of the wooden support dragging the glue layer into strain, Mecklenburg (1998) ;these RH variations, happening in the sacristy of Goa Cathedral, lead to the swelling and shrinking of this sizing layer and, consequently to the detachment of the ground layer in some areas of the non-conserved paintings (Table 1). Animals (owls, bats, squirrels, pigeons, insects) that inhabit the sacristy room deposit over the paintings external biological contamination contributing to its degradation. Discussion How to preserve a set of paintings made with European materials and taken to South Asia in the 16 th century? Preventive conservation concerns the procedures for reducing the causes of degradation of this set of paintings. Microclimatic conditions of the sacristy room show in the previous evaluation of the thermo-hygrometric conditions values that serve only as reference for a preliminary evaluation. Only knowing the history of the climate of the room it will be possible to study and evaluate the temperature and humidity ideal for this set of paintings, Casanovas (2006) .However, it should be taken into account that the variation of RH fluctuated more than 10% only in this preliminary evaluation period, and there was no "hygroscopic inertia", Casanovas (2006) in the room. Microclimatic calculations of the room should be taken for a larger period, trough different seasons, to achieve microclimatic parameters knowledge to preventive control for preservation of this set of paintings. We should also take into account the fluctuations in the monsoon season rainfall, when RH generally increases, from June to September, Menon (2013) .Light conditions of the room present a system of natural light through four big windows that allow daily fluctuations of light and RH since they are permanently open and have no curtains. By closing and caulking these windows and incorporating a system of full screen curtains with anti-UV protection can avoid the entry of direct natural light over the paintings and fluctuations in RH may diminish considerably, since uncontrolled natural light and air inlets are one of the major causes of ambient humidity, Casanovas (2006) . The artificial lighting system is composed of tubular fluorescent lamp sets embedded in the walls of the room. In the measurement of the lighting conditions were obtained with the curtains totally closed and with the artificial lighting system connected between 250 to 350 lux. It should be avoided high and continuous lighting levels, Herráez (2014) . The room doors and windows must remain closed in order to stop air currents and oscillations of the microclimate, avoiding also the passage of biological contaminations. The hanging of the paintings should be made with appropriate systems, with resistance to support the weight of each painting; to avoid condensation in the paintings verso it should not be directly leaning against the wall. 4.