Use of the ”Video Spectral Comparator 6000” as a non-destructive method for pigment identification -An experiment

Abstract

The Video Spectral Comparator 6000 (VSC) is a machine by Foster + Freeman. The machine has many functions in which it uses different light sources to examine documents, and is usually used as a forensic tool to check the validity of valuable documents. The machine is a comparator, and it is often used to compare one set of images or spectra up against another. In this experiment, five functions of the VSC were selected to see if they can be used to identify pigments. These functions were Visual-image, UV-image, Visual spectra, UV-spectra and Spot (fluorescence). First a small reference library was made of 15 Winsor & Newton Artists’ Watercolor pigments of the colors blue, brown and green used in the 1920s. The pigments were recorded into the VSC and then six unknown pigments, from five aquarelles by Alexey Zaitzow, were recorded in the same manner. These were then compared with the references. To check the validity of the comparisons, the unknown pigments were also tested with a Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS). Only four of the unknown pigments could be compared properly with the references, since two of the colors were mixtures. Since the comparative material got smaller, additional samples were made by Derwent Studio pencils and Winsor & Newton tube colors. The result of the experiment was that the visual image and the UV-spectra functions were not suitable for pigment identification. The UV-image and Spot (fluorescence) functions might become useful with further tests and an expansion of the reference library. The visual spectra function proved to be most suitable. It could correctly identify most pigments. In the cases were the spectra did not match, this might be because pigment composition was different from what the color name indicated. Therefore this function can probably be used for pigment identification. As background knowledge to the experiment, other non-destructive techniques have been gone through and there is an explanation of light and how it gives the sensation of color.