Identification of Synthetic Resins Used in Works of Art by Fourier Transform Infrared Spectroscopy

Abstract

Differentiation between the synthetic polymers used in former restorations of works of art and the original materials used by the artist is of great interest; such differentiation is needed to establish an adequate process of restoration for the work of art. A speci c method of sample preparation based on a ltration and depositionevaporation sequence is proposed, which permits the separation and preconcentration of the synthetic polymer that is being analyzed and avoids problems arising from the simultaneous interpretation of IR spectra obtained from com plex m ixtures of organic and inorganic compounds present in small artistic samples. In addition to the identi cation of characteristic IR absorption bands, quantitative diagnostic criteria based on two-dimensional diagrams of relative intensity of selected peaks have been developed. Standards of acrylic, alkyd, cellulose nitrate, epoxy, ketone, poly(vinyl acetate), polyurethane, silicone synthetic polymers and semi-synthetic wax used as binding media, adhesives, and coatings have been prepared by this proposed experimental procedure, and IR spectra have been obtained. Finally, several samples from paintings and artistic objects dating from the 16th to the 20th century have been analyzed, and synthetic and semi-synthetic organic materials have been successfully identi ed by comparison with the standards using the proposed m ethod of analysis.

Raman spectroscopy of synthetic organic pigments used in 20th century works of art

“…6,7 However, FTIR spectra usually contain bands from the various binding medium components and to some degree also from inorganic pigments. 8,9 Their relative contributions are dependent upon the quantitative composition of the particular formulation. Therefore, the identification of organic pigments from the complex FTIR spectra of painting samples proved to be difficult in practice.…”

Molecular Spectroscopy

“…However, infrared microspectroscopy allows paint samples to be examined with layers intact [Derrick et al, 1999;Derrick, 1995;Tsang and Cunningham, 1991]. Both inorganic and organic pigments have been studied [Bacci, 2000;Bruni et al, 1999;Casadio and Toniolo, 2001;Castro et al, 2003;Derrick et al, 1999;Derrick, 1995;Desnica et al, 2003;Domenech-Carbo et al, 2001b;Kuckova et al, 2005;Low and Baer, 1977;Marengo et al, 2005;Moya Moreno, 1997;Newman, 1979;Salvado et al, 2005;Shearer et al, 1983]. The embedding media include acrylics, polyesters, epoxies or wax.…”

Hydrofluoric acid pre-treatment of matte artists’ paints for binding medium analysis by Fourier transform infrared microspectroscopy

“…Although gas chromatography with mass spectrometry is the technique par excellence for the specific identification of organic media in artworks [1], in many museum laboratories FTIR spectroscopy may be the only method available to provide an identification of the varnishes, binding media, pigments, fillers and preparatory layers of paintings [2]. When the paints are underbound, as is the case in many matte paints and ground layers, the strong mid-infrared absorptions from the copious fillers, pigments, and matting agents can interfere with the identification of the binding medium [3][4][5][6][7]. The same issue has been raised in forensic laboratories challenged with identifying the paint binders in evidence [8].…”

“…Solvent extraction is a common method for preparing underbound paint samples for binding medium analysis [3][4][5][6][7]. If the sample is large, the aqueous or solvent extract can be spun down in a centrifuge, and a portion of the supernatant dried on a sampling substrate suitable for FTIR analysis.…”

“…Mixed media paints may also require multiple extractions to identify the full array of binders [3][4][5][6][7]9], and there is no way of knowing if the sample was leached of all its organic components.…”