9/6/2023 0 Comments Inpaint 6.0Metal carboxylates are also formed between terpenoid acids-deriving from plant resins used in coatings, varnishes and as ingredients of paint binders, and certain cations, as it has been discussed in several publications. Moreover, in manufactured oil paint formulations, since the 19th century, metal soaps (most commonly Zn and Al stearates) have commonly been added to facilitate the dispersion of pigments into the medium. Metal soaps are known to be spontaneously formed in artistic oil paintings, as a product of reaction between the excess of carboxylic acid moieties released by the hydrolysis of triglycerides as well as the oxidative cleavage of unsaturated fatty acids, and the metal ions contained in certain pigments. 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. 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. 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. 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. 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.
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