How Can Ozone and Relative Humidity Affect Artists’ Alkyd Paints? A FT-IR and Py-GC/MS Systematic Study

Abstract

Knowledge of the chemical–physical reactions that determine the main degradation behaviour of artists’ alkyd paints represents one of the main problems within the museum exhibitions. The collection and interpretation of these data on degradation phenomena, especially after ozone exposure at different relative humidity values, can be useful for their conservation needs. Therefore, a systematic investigation of these materials may help achieve this goal. Firstly, surface-level identification of the main functional groups of ad hoc created and aged alkyd paints was performed using attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). Subsequently, these paints were investigated by pyrolysis–gas chromatography and mass spectrometry (Py–GC/MS), allowing for precise bulk identification of the organic compounds before and after accelerated ageing. A first successful attempt to provide quantitative Py–GC/MS data on alkyd-based paints is here presented and discussed. Comparing the results, it was possible to obtain new insights into the degradation behaviour of alkyd paints when exposed to ozone, allowing us to devise specific preventive and conservation strategies for these artistic materials.

Data Fusion Approach to Simultaneously Evaluate the Degradation Process Caused by Ozone and Humidity on Modern Paint Materials

“…A further demonstration of the polymer degradation by chain scission is given by the increase in absorption around 3500 cm −1 related to the formation of carbonyls and carboxylic acids [55]. As already demonstrated in a parallel study [56], this phenomenon is explained by the intrinsic properties of the water deposited on the polymeric surface and the ozone reactivity in a humid environment. Depending on the humidity value used, the layers of superficial water can deposit differently.…”

Integrated Investigations to Study the Materials and Degradation Issues of the Urban Mural Painting Ama Il Tuo Sogno by Jorit Agoch

“…Stratigraphic sequences observed on the painting samples under PLM in reflected light appear quite simple, consisting of two painting layers (Sample JA1, Figure 3a), with an orange layer (layer b) which is above a whitish one (layer c) and directly applied on the mortar (layer a) and three painting layers (sample JA2, Figure 3b) with pinkish (layer b) purple (layer c), and pinkish (layer d) layers where the layer directly applied on the morta appears thicker (35)(36)(37)(38)(39)(40) The sample JA4 at the microscopic observation yields a stratigraphic sequence made of two layers (Figure 4): (b) a pink, irregular, and discontinuous pictorial layer (0-50 µm containing some rounded particles visible under UV light and (a) a dark red/orange layer which typically shows a significant thickness of 70-120 µm and is composed of a series o thin coats where white particles are mixed with very-fine-grained red/orange particles The corresponding SEM-EDS results (Figure 5) for a portion of the sample stratigraphy allow us to identify titanium dioxide (PW6), iron oxides (PR101) or hydroxides (PY42) and a few silica particles in layer b; mainly iron oxides or hydroxides were detected in layer a. Iron-based pigments and titanium dioxide are very common pigments in modern paints [16,26]. The sample JA4 at the microscopic observation yields a stratigraphic sequence made of two layers (Figure 4): (b) a pink, irregular, and discontinuous pictorial layer (0-50 µm) containing some rounded particles visible under UV light and (a) a dark red/orange layer, which typically shows a significant thickness of 70-120 µm and is composed of a series of thin coats where white particles are mixed with very-fine-grained red/orange particles.…”

“…Benzoic acid ranges from 12 to 17% for RV100, RV136, and RV 97 and from 6 to 10% for RV205 and RV35. However, because benzoic acid, an aromatic monobasic acid, is more likely present as a stopping agent in the commercial formulation rather than due to a pyrolysis product of the polybasic acid [37], the comparison of the percentages of the major components of the Montana spray paints revealed a similar composition between them.…”

Preliminary approach to protect Street Art from environmental agents and gaseous pollutants

“…The main environmental agents that can lead to deterioration are temperature (T), relative humidity (RH) fluctuations, solar irradiation (UV-light), particulate matter, and gaseous pollutants. The latest research [9][10][11] show that gaseous pollutants have a significant impact on the chemical stability of painting materials. Degradation reactions vary depending on the type of gas under consideration, its combination with environmental humidified water, and their interaction with different polymeric materials and the pigments in the mixture.…”