CHARACTERIZATION OF YELLOW AND RED NATURAL ORGANIC COLORANTS ON JAPANESE WOODBLOCK PRINTS BY EEM FLUORESCENCE SPECTROSCOPY

As part of a project designed to systematically identify colorants on Japanese woodblock prints, excitation-emission matrix (EEM), or three-dimensional, fluorescence spectroscopy, equipped with a fiber optic probe, was used to characterize natural yellow and red organic colorants on 18th-century Japanese prints without taking samples. This analysis technique collected emission spectra in the visible region for a sequence of excitation wavelengths at nm steps from 250 to 600 nm. The resultant data set provided characteristic excitation/emission patterns that were used to identify several natural colorants, including safflower, madder, sappanwood, gamboge, flavonoids, berberines, and turmeric. In combination with other non-sampling methodologies, including x-ray fluorescence and fiber optic reflectance spectroscopy, most colorants on the prints were quickly and non-destructively characterized. Based on examination of 213 prints, several patterns of colorant use were observed. The prints often contained more than one yellow, red, or blue colorant. From 1781 to 1801, considered the Golden Age of the Japanese print, it was common to find multiple types of yellows, reds, and blues on a single print. The colorant madder was identified on many of the prints, while gardenia and berberine-containing dyes were found on none. This paper presents the theory, experimental parameters, and limitations of the EEM fluorescence technique. The technique is illustrated using the analysis results of four Japanese woodblock prints.