Identification of synthetic resins used in works of art by Fourier transform infrared spectroscopy

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 specific method of sample preparation based on a filtration and deposition-evaporation 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 complex mixtures of organic and inorganic compounds present in small artistic samples. In addition to the identification 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 identified by comparison with the standards using the proposed method of analysis.