The Use of Ft-Ir Spectrometry for The Identification and Characterization of Gesso-Glue Grounds in Wooden Polychromed Sculptures and Panel Paintings

Abstract

Traditional Western techniques for gilding of polychromed sculptures and panel paintings include the use of grounds prepared by the application of a first layer of gesso grosso followed by a gesso sottile layer, as described by Cennino Cennini in his treatise on painting techniques. These techniques have been used in Italy since the Middle Ages, and were later adopted by many artists in regions of the new world under Spanish and Portuguese rule, sometimes with local variations in materials and techniques. This article discusses the use of Fourier transform infrared spectrometry (FTIR) for the identification of inorganic materials present in the grounds of Baroque wooden polychromed sculptures from Minas Gerais, Brazil. This technique allows the quantitative analysis of the separate layers of the grounds, with respect to the anhydrite/gypsum ratio present in the sample. The technique has several advantages over the one currently used (Debye-Scherrer chamber for x-ray powder diffraction). FTIR spectra can be obtained in a few minutes allowing quantitative results, while x-ray diffraction usually takes more time and does not give accurate data for quantitative studies. The article also discusses the results of the studies of the grounds in Brazilian polychromed sculptures and compares the original Italian technique with Portuguese and Spanish techniques and its variations in Brazil. -- AATA