EEM analysis of Ukiyo-e prints
Overview
Specific red or yellow dyestuffs may display characteristic EEM graphs that can be used to compare with graphs from prints to identify different dyestuffs. For Japanese prints, two of the three likely red organic colorants fluoresce strongly (safflower and madder) while the third only weakly (sappanwood) and their EEM fluorescence is the only means for at least tentatively identifying these colorants. Even so, there is some some uncertainty in interpreting results. In fact, different fluorescence spectrophotometers may also produce slightly different results.
EEM Reference Spectra
To make reference samples for EEM analysis, The printing dyes were prepared from known colorants using traditional methods. They were then printed on papers of similar type and surface preparation as those used in Japanese prints. All materials and techniques were kept as close as possible to the historically known methods and materials in order to provide reasonable points of comparison of the fluorescent colorants in the prints. This was done because the fluorescence of specific materials can be affected by concentration of the dye as well as by other components, organic and inorganic, known or unknown, mixed with the dyestuffs. Because of this, not every example of a specific dyestuff will produce exactly the same EEM contour map. In addition, while analysis of reference samples prepared in the lab suggest that the major reds (safflower, madder and sappanwood) should be able to be distinguished, this is not always the case. As a characterization aid, the excitation and emission spectra can be extracted from the EEM data file. These better show the excitation and emission of a material that the 3D contour maps.
3D EEM plot for Safflower 
3D EEM plot for Madder 
EEM reference spectrum of Sappanwood 
Excitation and emission maxima for safflower, madder, and sappanwood]]
Analysis
Analyses sometimes show spectra that do not very well match reference spectra obtained from any of the pure organic reds. This could be for many reasons, such as paper types, aging, discoloration, dye preparation methods, etc. In some instances, reds bleed through the paper during printing and EEM data can optimally acquired from the front and back of a red area, then compared. In some cases the colorant produces a clearer spectrum from the back. But in other cases, we found that the front and back differ from one another (usually in a subtle fashion), in the type of colorant, indicating that a mixture of two main reds was probably used; one of which bleeds through the paper more easily than the other. This possibility illustrates the complexities and potential uncertainties, in the interpretations of fluorescence data from organic reds in Japanese prints. It also appears that mixtures of more than one of these three may be been often used, especially the combination of madder and safflower. Examples, for such mixtures are shown below with EEM graphs
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