| Abstract: | SUMMARIES. Ultraviolet-visible reflectance spectroscopy is a rapid and accurate technique for the investigation of painted surfaces. The use of a high efficiency beveled-tip fiber optic probe and a pulsed xenon source gives improved detection efficiency and minimizes the interference from ambient light, eliminating the need to shield the analyzed area and allowing non-contact, non-invasive analysis. Thin washes of organic colorants, often impossible to sample, are ideally suited to this kind of analysis. This study describes the in situ identification of indigo, Prussian blue and a red insect dye (cochineal carmine or lac dye) in two paintings by Katsushika Hokusai.
CONCLUSION. The coupling of an inexpensive and innovative UV-visible spectrophotometer with a fiber optics probe of advanced design made it possible to obtain reflectance spectra from minute details on the surface of a painting in a relatively short time and without interference from ambient light, thus removing the need for shielding or contact between probe and analyzed object. The technique is well suited to the analysis of organic dyes and thin washes of colorants on oriental paintings, and in particular cases it can identify mixtures. In general, we found that it gave the best results on areas of light paint application and, consequently, fairly high reflectance; in this sense it tends to comple¬ment methods based on removed samples, which are more likely to be feasible in more heavily painted areas. The application of fiber optics reflectance spectroscopy to two paintings by Katsushika Hokusai resulted in the identification of indigo and of a mixture of indigo and Prussian blue in the two paintings. An organic red pigment was found on the paintings and tentatively identified as either cochineal or lac dye. These results could not have been obtained with any other single technique, given the extremely small amount of the pigments present on the paintings. |
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