Raman

Analytica Chimica Acta 407 (2000) 261–274

Analysis with micro-Raman spectroscopy of natural organic binding media and varnishes used in art
P. Vandenabeele ∗ , B. Wehling, L. Moens, H. Edwards, M. De Reu, G. Van Hooydonk
Laboratory of Analytical Chemistry, University of Ghent, Proeftuinstraat 86, B-9000 Ghent, Belgium Received 29 June 1999; received in revised form 22 October 1999; accepted23 October 1999

Abstract Micro-Raman spectroscopy (MRS) allows the identification of binding media and varnishes in paintings. This non-destructive micro-analytical method has been used for the recording of spectra (1800–200 cm−1 ) of different types of proteinaceous (albumin, casein, gelatin, isinglass, fish glue), polysaccharide (starch, gum arabic, tragacanth, cherry gum), fatty acid (beeswax,linseed oil, poppy-seed oil, walnut oil, sunflower oil) and resinous media (shellac, dammar, colophony, sandarac, copal, elemi, Venice turpentine, Strasbourg turpentine, amber, mastic, dragon’s blood, gamboge). The Raman spectra can be used as a reference for fingerprinting unknown binders and varnishes. This is demonstrated by the identification of the binder and pigment in a sample of a medievalilluminated manuscript. ©2000 Elsevier Science B.V. All rights reserved.
Keywords: Binding medium; Varnish; Non-destructive micro-analysis; Micro-Raman spectroscopy (MRS); Paintings; Medieval manuscripts

1. Introduction Many problems in the conservation of paintings arise from changes in the binding medium or in the varnish layer [1]. In many cases the analysis of paintings or paint samplesonly takes into account the identification of the (inorganic) pigments. Due to this fact many paint analyses are performed using X-ray fluorescence (XRF) or related techniques [2–6]. With these techniques, the light elements often cannot be detected sensitively and the elemental analysis is insufficient to distinguish between organic substances. Therefore, X-ray methods are considered to beinappropriate for the analysis of binding media and varnishes. Nevertheless, von Bohlen and Meyer [7] demonstrated
∗ Corresponding author. Tel.: +32-9-264-66-23; fax: +32-9-264-66-99. E-mail address: peter.vandenabeele@rug.ac.be (P. Vandenabeele).

the possibility of characterising different varnishes via the concentration of heavier elements, determined by total-reflection X-ray fluorescence (TXRF).Although this method has been used successfully for the identification of violin varnishes, it is not suitable for painting varnishes or glazes (i.e. pigments, mixed with varnish, giving a transparent coloured layer) where the elements present in pigment particles mask the heavy elements in the varnish. Separation methods (such as gas chromatography, capillary electrophoresis and liquid chromatography),mass spectroscopy and hyphenated techniques are well suited for the analysis of binding media [8], but the relatively large sample consumption, the extensive sample preparation and the multi-parameter operating conditions are disadvantageous. In this type of analysis, the sample is consumed, making it impossible to repeat and confirm the analysis, unless the artefact is sampled again. Althoughvibrational

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P. Vandenabeele et al. / Analytica Chimica Acta 407 (2000) 261–274 Table 1 Overview of the media used for recording Raman spectra Name Egg white Casein Gelatin Isinglass Fish glue Starch Gum arabic Tragacanth Cherry Gum Beeswax Linseed oilPoppy-seed oil Walnut oil Sunflower oil Shellac Dammar Colophony Sandarac Copal Elemi Venice turpentine Strasbourg turpentine Amber Mastic Dragon’s blood Gamboge Supplier Local supplier Kremer Vahin´ e Kremer Kremer ANCO Kremer Kremer J. Ham Kremer Gouden Pluim Märch A. L’Olivier Delhaize Gouden Pluim Gouden Pluim J. Ham J. Ham Gouden Pluim Kremer Kremer Kremer – Kremer HMB Kremer Pre-treatment/remarks...