HIGH RESOLUTION-MAGIC ANGLE SPINNING (HR-MAS) NMR ANALYSIS OF SOLID PAINT VARNISHES Kartsonaki Eypraxia1, Spinella Alberto2, Knuutinen Ulla3, Caponetti Eugenio2, Anglos Demetrios1,4 and Spyros Apostolos1 1 Chemistry Department, University of Crete, Heraklion Crete, Greece, [email protected]; 2 Centro Grandi Apparecchiature, University of Palermo, Palermo, Italy, [email protected]; 3 Helsinki Metropolia University of Applied Sciences, Helsinki, Finland, [email protected]; 4 Institute of Electronic Structure & Laser, FORTH, Heraklion Crete, Greece Keywords: varnishes, NMR spectroscopy, solid state Objectives. The word “varnish” - sometimes the word “lacquer”- is used to describe any type of surface coating. Varnishes are made of resins which contain mainly terpenes. Resins are produced by plants or they can have fossilized origin. Historically, there are three distinct types of historic varnishes: spirit, essential oil, and fixed-oil varnishes based on their use and application. Varnishes are important in cultural heritage materials research because of their role in protecting the outer surface of paintings and other artifacts . The identification and compositional analysis of varnishes can assist the restoration process during conservation treatments and provide information about the state of a painting , and previous restoration attempts. In this study we examine the potential of HR-MAS NMR spectroscopy for the direct identification and analysis of natural terpenoid resins in model paint varnishes directly in the solid state and without any sample treatment. Experimental. Resin samples (copal, dammar, colophony, mastic, sandarac) were used to prepare model aged varnishes as follows: resins were dissolved in acetone, mixed with linseed oil in 50-50 ratio per weight, cast on glass plates and aged in the laboratory under ambient conditions for two years. HR-MAS 1D and 2D NMR spectra were obtained with a Bruker Avance II 400 MHz spectrometer. Results. The 1H HR-MAS NMR spectra of solid model varnishes were found to be dominated by their linseed oil component, and thus to appear practically identical. However, it was found that the 2D HR-MAS NMR correlation spectra (either 1 H-1H gCOSY or 1H-13C gHSQC) of all varnishes contain cross peaks that can be used to identify the presence of a specific resin in the varnish. These peaks were assigned by comparison with 2D NMR spectra of pure resins in solution. As an example, Fig. 1 depicts the 2D proton correlation NMR spectrum of aged solid copal varnish. The two peaks indicated by arrows were assigned to the side chain of copalic acid, a constituent of natural copal. Using either gCOSY or gHSQC HR-MAS 2D spectra, it was possible to successfully identify all five resins in aged model varnishes prepared with linseed oil. Fig. 1 HR-MAS 1H-1H gCOSY NMR Conclusions. The examination of several model varnishes based on drying oil via HR-MAS NMR spectrum of a solid copal varnish spectroscopy shows that 2D NMR spectra can be containing linseed oil that was aged for used for the identification of the natural resin two years. Arrows denote peaks originating used in the varnish, even in the case that the from copalic acid, a copal component. varnish has been considerably aged. Further studies using varnishes sampled from works of art are in progress. References. 1. JS Mills, R. White, The organic chemistry of museum objects, 2nd edn., Butterworth Heinemann, Oxford, 1994. 2. A. Spyros and D. Anglos, Study of Aging in Oil Paintings by 1D and 2D NMR Spectroscopy, Analytical Chemistry, 76 (2004), 4929-4936.