Modeling the Evolution of Crosslinked and Extractable Material in an Oil-Based Paint Model System.

The construction of mechanistic models for the autoxidation of fatty acid or ester substrates found in oil paint binders is a challenging undertaking due to the complexity of the large crosslinked species that form, and the small molecules that volatilize. Building models that capture this product diversity are made possible by automating the process of network generation. This work presents a microkinetic model for the autoxidation of ethyl linoleate catalyzed by cobalt(II) 2-ethyl hexanoate. The mechanism size was controlled by using a rate-based criterion to include the most kinetically relevant reactions from among the millions of possible reactions generated. The resulting model was solved and compared to experimental metrics. Quantities such as hexanal production and the consumption of unsaturated moieties were in good agreement with experiment. Finally, the model was used to explore the effect of the catalyst concentration and temperature on key measurables.

Pretreatment strategies for SERS analysis of indigo and Prussian blue in aged painted surfaces.

Surface-enhanced Raman scattering (SERS) spectroscopy is increasingly applied to the identification of organic colorants in cultural heritage objects because vibrational fingerprints can be measured from microscopic samples. However, the development of SERS into a reliable, broad-spectrum method for art analysis requires the study of a wide variety of organic and inorganic colorants as well as colorant mixtures in paint. Here, we demonstrate reliable protocols for SERS-based identification of insoluble indigo, Prussian blue (PB), and mixtures thereof in aged painted surfaces. The use of simple salts and acids for sample pretreatment is evaluated. High-quality SERS spectra of PB and indigo are elucidated upon sample pretreatment with H(2)SO(4). In several cases, SERS spectra of the colorants could not be obtained without sample pretreatment. We demonstrate the use of H(2)SO(4) to solubilize PB as well as perform an in situ conversion of insoluble indigo to soluble indigo carmine (IC) on indigo, indigo oil paint, and actual samples from historic painted surfaces. A microscopic H(2)SO(4)-treated sample from the Portrait of Evelyn Byrd produced a SERS spectrum that is consistent with a mixture of PB and IC. To our knowledge, this work represents the first SERS spectrum of indigo in oil paint and the first simultaneous detection of a mixture of blue organic and inorganic colorants in a single art sample using SERS.

Identification of organic materials in historic oil paintings using correlated extractionless surface-enhanced Raman scattering and fluorescence microscopy.

A novel spectroscopic approach, correlated surface-enhanced Raman scattering (SERS) and fluorescence microscopy, is used to identify organic materials in two 18th century oil paintings. The vibrational fingerprint of analyte molecules is revealed using SERS, and corresponding fluorescence measurements provide a probe of local environment as well as an inherent capability to verify material identification. Correlated SERS and fluorescence measurements are performed directly on single pigment particles obtained from historic oil paintings with Ag colloids as the enhancing substrate. We demonstrate the first extractionless nonhydrolysis SERS study of oil paint as well as the potential of correlated SERS and fluorescence microscopy studies for the simultaneous identification of organic colorants and binding media in historic oil paintings.