The analysis of naturally and artificially aged protein-based paint media using Raman spectroscopy combined with Principal Component Analysis.

The analysis of protein-based paint media used in paintings is presented using micro-Raman spectroscopy, carried out with a diode laser emitting at a wavelength of 785 nm. Following a contextualisation of the analysis and ageing of protein-based binding media, a consideration of the effects of artificial ageing using visible light on the Raman spectra of binding media is given and the interpretation of changes to the Raman spectra of selected binding media is presented. Bands associated with aromatic amino acids are most affected by ageing, but spectra retain diagnostic information for the identification of proteins. Specific changes to the spectra of dairy and collagen-based binding media are described and explained with reference to the oxidation of amino acids. A multivariate approach using Principal Component Analysis has been chosen for the assessment of the bands in C-H stretching region for which a large set of over 150 spectra were recorded from artificially and naturally aged binding media which included egg white, egg yolk, milk and casein, and collagen-based glues from rabbit skin, ox bone, parchment and sturgeon bladder. Raman spectroscopy has been used for an assessment of the effects of ageing and the detection of degradation due to exposure of light. Multivariate analysis has allowed the differentiation between a large data set of spectra of naturally and artificially aged binding media. Copyright (c) 2008 John Wiley & Sons, Ltd.