Browsing by Author "Hornytzkyj, Seppo"

Artists’ pigments identified from paintings can be used for dating paintings, for the examination of painting techniques of different artists and thereby aiding the attribution of their artworks, for recognizing copies and forgeries and for answering questions and solving problems related to conservation and restoration of paintings. From an analytical point of view, the most important pigments are those known as traditional artists’ pigments that had come into use before the 1920’s, as most analytical research in the field focuses on paintings that have been made before this. The main methods used for the identification of traditional artists’ pigments are SEM-EDS, EDXRF-spectrometry, Raman spectrometry and XRD. Polarized light microscopy has mainly been used for the visual characterization of pigment particles and thin-sections taken from paintings. If applied to the identification of pigment particles, a complementary method has always been used to confirm the result. Polarized light microscopy allows the assessment of a large variety of optical properties of pigment particles. There is, however, no systematic compilation of them available. The current work was launched to examine whether polarized light microscopy can be utilized to identify pigment particles in traditional artists’ pigments based on their optical properties only. I applied standard polarized light microscopy augmented by IR microscopy, the Chelsea filter technique, and phase contrast microscopy. The research material of the work comprises the ten most common traditional blue artists’ pigments: azurite, synthetic azurite, lazurite, synthetic lazurite (ultramarine) cobalt blue, cerulean blue, smalt, Egyptian blue, Prussian blue, and indigo. Most of the pigments examined were acquired from 1440-1915 oil paintings on wood, canvas, or paper; these paintings had been under conservation and restoration in the Ateneum and Sinebrychoff art museum in 2000--2012. Pigment particles were detached from the paintings with a tungsten needle under a binocular microscope and were transferred into a thermoplastic immersion liquid for polarized light microscopy. The identity of all the examined pigment particles was confirmed using SEM-EDS or an FTIRspectrometer. The results obtained were compared to pre-existing literature data, and a two-fold classification scheme for optical properties of pigment particles is proposed, primary and secondary. The former are found in all of the examined pigment particles, whereas the latter are commonly observed but not necessarily present in every pigment particle. Primary properties are the particle size, particle shape, particle size range, optical sign, extinction, refractive index, relief, color observed with the Chelsea filter, IR transmission and IR luminescense. For each of the blue pigments examined, five to seven primary properties, specific to the pigment, could be observed. This allows optical identification of the ten blue pigments. The technique may also be developed for the identification of other than blue artists’ pigments.