# Degradation Products Assessment of the Wooden Painted Surfaces from a XVIIth Heritage Monastery
## 3 Results and Discussion  
In oil painting conservation, the occurrence of metal soaps through the reaction between metallic ions and saturated fatty acids is currently a growing concern. In the case studied in this paper, large deposits of metallic soaps were found on the exposed surface of the paintings, visible by optical microscopy and stereomicroscopy. However, some case studies have been reported where saturated fatty acids migrated from the paint layer and crystallized on the paint surface. All these processes affect both the oil painting aspect and their structural integrity. Additionally, the formation of metallic soap created a painted surface with protrusions, visible by optical microscopy, in good agreement with the specialized literature [24]. For identifying the metallic soap and the degradation products of these icons, the following directions are followed in this work:  
(1) The study of macro and microscopic aspects that reveal the current state of icon paintings. In this sense, discussions are addressed about the visible changes of the painting and the related microscopic findings: stratigraphy, the presence of efflorescence and all defects detected using optical microscopy and SEM analysis;  
(2) The characterization of the materials used, original pigments and binders, but also those added during the previous restoration procedures;  
(3) The identification of degradation products (metallic soaps and other efflorescence). The stratigraphic layers of representative paint fragments from each sampling location were examined with an optical microscope and stereomicroscope. All samples contained a colored layer (blue, green, or red) and a white base layer, with possible intermediate layers of gray or black paint. The collected samples are composed of several layers of paint, most likely due to the repeated interventions that took place over time. The pigments and the places where they were taken are shown in Table 1. In this table are also attached the related chromatic parameters, as useful data in classifying these pigments in the color classes. The granular texture observed in the images provided by optical microscopy can be a first explanation for the formation of metallic soaps. In Figure 3, images of the variously painted areas are presented, and aggregates of metallic soaps that have penetrated/protruded through the paint surface, have been identified. Metallic soap efflorescence, observed by OM, appears as transparent or whitish opaque masses, with a circular shape, with a diameter between 10 and 200 \(\upmu\)m and can reach up to 500 \(\upmu\)m or even larger [17]. In our case, the opaque mass has the size of 30-50 \(\upmu\)m. This metallic soap can penetrate the surface of the pictorial layer, migrate to the surface of the painting and lead to the formation of crusts of lead carbonates, hydroxy chlorides, sulfates and sometimes oxalates, increase the transparency of the pictorial layer, affect the wooden support allowing artists to become visible in some paintings in oil [25]. Aggregates with small dimensions are possible and lead to an expansion of the volume, in order to later pierce the surface layers and erupt on the surface. In some cases, the damage caused by metallic soaps appears as dark spots, most likely attributed to preservation treatments and can be due to the accumulation of dirt and layers of aging varnishes and coatings, and some pustules appeared on the surface. The microscopic analysis of the paint samples detached from these icons corroborated with WDXRF and EDS results, and highlighted the presence of zinc soap as a fluffy deposit formed at the painting surface; this being the cause of the deterioration of hundreds of oil paintings dating from the 15 th to the 20 th centuries [38; 39]. OM is completed with stereomicroscopy, which allows to clearly observe the white layer of metallic soaps formed at the pigment surface, Figure 4. Additionally, by using the microscope tool it was possible to measure the size of the white deposit from the surface painting.