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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1. Introduction The first altarpiece of Goa Cathedral, devoted to St Catherine of Alexandria and assigned to the painter Garcia Fernandes, was produced in Lisbon circa 1530 and taken to Goa shortly after Serrão (2011), Reis-Santos (1957) .In the seventeenth century this altarpiece was replaced by a gold leaf carved altarpiece. The seven remaining paintings, besides being exposed to climate changes when brought by boat from Portugal a century before, were at that time moved from its original altarpiece and kept in another place, trying to adapt its equilibrium to new changes in relative humidity (RH). In 1940, three of the paintings of this altarpiece were brought to Portugal for an exhibition of Portuguese Old Masters, and were restored at that time, Reis-Santos (1957) . These three paintings are nowadays in better state of conservation than the others. The other four of the seven remaining paintings were not restored, but repainted over their losses and part of the original. These are the most damaged paintings, showing significant loss of the original chromatic layer. Studies show that microclimatic stability is essential for painting preservation since moisture correspond to one of the most important reasons in the delaminating of glue size, calcium sulphate grounds and paint layers, Mecklenburg (1998) .Adhesion bonds are disrupted by high moisture, contributing to a physical separation of the materials, Mecklenburg (1998) . Osmotic processes, by balancing the concentration of water-soluble materials in the ground, paint and varnish layers may affect fragile areas of the chromatic layers, increasing lacunae and lifting of flakes, Nicolaus (1999) . Direct contact with water by condensation or aggressive oscillations in relative humidity destroys the bond between grounds, pigments and binding media. Concerning ground layers, too little animal glue binder in the calcium sulphate ground layers promote low cohesion and adhesion of this layer, Mecklenburg (1998) .Old Masters knew already that a strong glue would damage the painting, as stated in a old Portuguese treatise of “Arte da Pintura”, wrote by Philippe Nunes in 1615,where the author advise that sizing layer,the first glue layer given over the wooden panel, should not be “too strong” , Nunes (1982) . The conservation of this altarpiece may be compared to the altarpiece of Bartolomeu Joanes chapel of Lisbon Cathedral, devoted to “São Bartolomeu”, assigned to the same painter and being constructed in the same decade, Reis Santos (1957) .This altarpiece is made with similar materials, Ribeiro (2000), Alves (2001) and is notorious the better conservation of this last one, restored in the last decade of the twentieth century. Its preservation suggests that the building assures the necessary conditions to its maintenance with a minimum of thermal stability, assuring the doors and windows to be closed and water tightness, such as walls, Casanovas (2006) . Being carried by sea from Portugal to Goa while recently made paintings, still having a high percentage of unlinked binding media, these paintings could be classified as “adapted” to climate changes , Nicolaus (1999) .Although, nowadays in a high RH environment, these paintings cannot be returned to moderate RH climate without degradation, Mecklenburg (1998) . 2. Materials and methods RH was measured through a psychrometric scale relating room temperature and humidity . Evaluation was performed with a psychrometer of the Brannan brand (England) and confirmed with manual and digital thermometers, taking into account the "historical climate" of the collection, Herráez (2014), Asociación Española de Normalización y Certificación (2011) . Illuminance (Lux) of the room were measured with a Amprobe Digital illuminance Meter,Model LM-80. A mobile microscope 3 " LCD 8,5 Mega Pixels 20-500x,Digital LCD with VGA capture, Micro SD card storage and a MicroCapture Pro software was used to obtain macro-photographs of the chromatic layers and its degradation. Samples were mounted using an Epofix embedding resin with hardener and dry polished with sequentially finer grades of Micro-mesh abrasive cloths. Materials were characterized using an array of techniques: Cross-sections were studied by optical microscopy (OM) with a Leica DM 2500M optical dark field and dark-field microscope coupled to a digital camera Leica MC170HD and images were taken at different magnifications (from 100× to 500×). A Bruker diffraction system microdiffractometer (Bruker AXS, D8 Discover) was used to perform Micro-X-ray Diffraction. This microdiffractometer is equipped with a one-dimensional Lynxeye detector, a Goebel mirror, a laser video sample alignment system and a motorized XYZ stage. Diffraction data were re gistered using Cu Kα radiation, tube running at 40 kV, 40 mA, with the incident beam collimated to 1mm diameter. XRD patterns were measured in the range 5º to 75º 2  , a step size of 0.05º, with a recording time of 1800s for each step. International Centre for