Identification of Or~anicColorants in Art Objects by Solution ~pectrophtometr y Pigments Fred W. Billmeyer, Jr.', Romesh Kumar and Max Saltzman Rensselaer Polytechnic Institute, Troy. NY 12181
Previous articles (1-3) on chemistry and artists' colors have pointed out that most of the pigments in the artists' palette in classical times were inorganic in nature. Only occasionally was an organic substance used, and until the synthesis of the first synthetic dye, mauve, by Perkin in 1856, these were lakes of natural dyes.2 In later years synthetic dyes were converted to lakes and anneared occasionallv in artists' paints.
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have been developed, some 250 are produced commercially, and we have identified over 60 of these in modern artists' paints. Each of these pigments contributes not only its masstone color-as it appears straiebt from the tuhe-but its own characteristic beh&ior whenmixed with white, black, and other colors, its own permanence properties, and many more individual characteristics that influence the artists' painting process and the properties of the final painting itself. We accept the premise, which we admit is not always true, that artists should know something about the pigments they are using: if not the details. thev should a t least know how their to discuss aliphases of this problem in the present paper, but it should be clear that a simple means of identifying organic the artist uses. Not only is he concerned with the artist's palette and painting habit, but his work can he made easier in the examination, preservation, and restoration of paintings if he is aware of the pigmentation used. Obviously, the identification of organic pigments in finished paintings requires micro-scale techniques. The obiective of the research described in this paper has been to dkvelop a simple, rapid identification technique for oreanic uiements. capable of being utilized on a micro scale. ~ ; c h a technique is not designed for use by the artist, but by pigment and paint manufacturers, testing laboratories, and of art,.~ ~ndustrial ~- ~ ~ colorists also find the techniuue valuable in ~
the coloring of paints, plastics, textiles, papers, inks, and many more products. Method
The method of solution spectrophotometry for the identification of organic pigments takes advantage of their solubility in one or more organic solvents. A small amount of the paint, from the tube, a test painting, or a minute speck from the edge Author to whom inquiries should be directed. A lake is a water-insolublepigment formed from a water-soluble dve " bv salt formation or chelation. in which the vresence of a substrate such as hydrated aluminum oxide is necessary and in which the sub strate forms an integral part of the lake. 2
