Investigating the Photocatalytic Degradation of Oil Paint using ATR-IR and AFM-IR

Abstract

As linseed oil has a longstanding and continuing history of use as a binder in artistic paints, developing an understanding of its degradation mechanism is critical to conservation efforts. At present, little can be done to detect the early stages of oil paint deterioration due to the complex chemical composition of degrading paints. In this work, we use advanced infrared analysis techniques to investigate the UV-induced deterioration of model linseed oil paints in detail. Subdiffraction limit infrared analysis (AFM-IR) is applied to identify and map accelerated degradation in the presence of two different grades of titanium white pigment particles (rutile or anatase TiO). Differentiation between the degradation of these two formulations demonstrates the sensitivity of this approach. The identification of characteristic peaks and transient species residing at the paint surface allows infrared absorbance peaks related to degradation deeper in the film to be extricated from conventional ATR-FTIR spectra, potentially opening up a new approach to degradation monitoring.

Investigating the effect of artists’ paint formulation on degradation rates of TiO2-based oil paints

“…The paint compositions of each run within experiments I, II and III respectively are reported in the result tables of "Results" section. Paint was prepared following a protocol commonly used in industry and in other studies [1,2] in order to achieve reproducible and smooth paints of a fixed layer thickness. The paint mixture was pre-mixed with a palette knife and subsequently mixed on a glass-plated paint mill (automatic muller from an unknown brand) twice for 25 rotations, with a weight of 5 kg.…”

“…The degradation of titanium white artists' oil paints has been under investigation in recent years [1,2]. This degradation is of interest because, while it is expected to occur, it is not yet commonly observed.…”

“…metal stearates or drying agents) and the binder (in this study linseed oil) [26]. Most earlier investigations have focused on pure titanium whitebinder mixtures to elucidate degradation phenomenology [1,2,23,25,27]. However, for the investigation of degradation rates, this constitutes an oversimplified formulation.…”

The white of the 20th century: an explorative survey into Dutch modern art collections

“…The reference set was based on readily available paints from other studies containing mixtures of different types of titanium white, titanium white mixed with zinc white, barium sulfate or calcium carbonate [16,18], as well as combinations of single-pigment layers (unpublished study). The dataset was extended with several crucial samples including layer combinations and mixtures with lead white and a calibration set for the Ba-L/Ti-K deconvolution.…”

“…The driving force was the need to know the extent of use of titanium white in relation to its risk of photocatalytic degradation [16][17][18]. The timing of titanium white becoming popular amongst artists is important, as it possibly relates to the quality of those pigments.…”