Two-step analytical procedure for the characterization and quantification of metal soaps and resinates in paint samples

Metal soaps and resinates are known to be spontaneously formed in artistic paintings, as a product of the reaction between aliphatic and terpenoid acids released by hydrolysis and oxidation of the organic media and certain cations contained in some inorganic pigments. In this paper we present an optimization and the validation of a GC/MS method for the qualitative and quantitative analysis of mixtures of terpenoid acids and aliphatic mono and dicarboxylic acids and metal carboxylates of terpenoid and aliphatic mono and dicarboxylic acids in the same paint microsample. This is based on a two-step analytical approach entailing the subsequent use of two silylating agents, N,O-bis(trimethylsilyl)trifluoroacetamide for the analysis of free acids and metal carboxylates, and 1,1,1,3,3,3-hexamethyldisilazane for the analysis of free acids. The application of this approach is possible because of the good stability at room temperature of the TMS derivatives of aliphatic and terpenoid species, characterized by high boiling points and relatively low vapour pressures. The method was then applied to the characterization of samples collected from two reference paint layers aged for 20 years, a paint sample taken from a pulpit, and sample of the varnish coating of a wooden writing desk, both from the second half of the seventeenth century

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

This study reports on the effect of artists’ paint formulation on degradation rates of TiO2-based oil paints. Titanium white oil paint exists in a multitude of different recipes, and the effect of the formulation on photocatalytic binder degradation kinetics is unknown. These formulations contain, among others, one or both titanium dioxide polymorphs, zinc oxide, the extenders barium sulfate or calcium carbonate and various additives. Most research performed on the photocatalytic degradation process focusses on pure titanium white-binder mixtures and thus does not take into account the complete paint system. Since photocatalytic oil degradation is a process initiated by the absorption of UV light, any ingredient or combination of ingredients influencing the light scattering and absorption properties of the paint films may affect the degradation rate. In this study three sets of experiments are conducted, designed using the design of experiments (DoE) approach, to screen for the most important formulation factors influencing the degradation rate. The benefits of using DoE, compared to a more traditional ‘one factor at a time approach’ are robustness, sample efficiency, the ability of evaluate mixtures of multiple components as well as the ability to evaluate factor interactions. The three sets of experiments investigate (1) the influence of the TiO2 type, (2) the impact of different mixtures of two types of TiO2, ZnO and the additive aluminum stearate and (3) the influence of common extenders in combination with photocatalytic TiO2, on the photocatalytic degradation of the oil binder. The impact of the formulation on the degradation rate became apparent, indicating the shortcoming of oversimplified studies. The protective effect of photostable TiO2 pigments, even in a mixture with photocatalytic TiO2 pigments, as well as the negative effect of extenders was demonstrated. Furthermore, the ambiguous role of ZnO (photocatalytic or not) and aluminum stearate is highlighted. Neither can be ignored in a study of degradation behavior of modern oil paints and require further investigation

Sparse coding can predict primary visual cortex receptive field changes induced by abnormal visual input

Receptive fields acquired through unsupervised learning of sparse representations of natural scenes have similar properties to primary visual cortex (V1) simple cell receptive fields. However, what drives in vivo development of receptive fields remains controversial. The strongest evidence for the importance of sensory experience in visual development comes from receptive field changes in animals reared with abnormal visual input. However, most sparse coding accounts have considered only normal visual input and the development of monocular receptive fields. Here, we applied three sparse coding models to binocular receptive field development across six abnormal rearing conditions. In every condition, the changes in receptive field properties previously observed experimentally were matched to a similar and highly faithful degree by all the models, suggesting that early sensory development can indeed be understood in terms of an impetus towards sparsity. As previously predicted in the literature, we found that asymmetries in inter-ocular correlation across orientations lead to orientation-specific binocular receptive fields. Finally we used our models to design a novel stimulus that, if present during rearing, is predicted by the sparsity principle to lead robustly to radically abnormal receptive fields