FORS analysis of Ukiyo-e prints

Overview

FORS reflectance spectra can readily distinguish between three common blue colorants used in Japanese woodblock prints (dayflower, indigo, and Prussian blue). Spectra for printed references of the three common blues are shown in Figures 1-3, along with spectra of each blue from a print (Figures 4-6). The paper used in the woodblock prints typically has a slight yellowish tint, thus for the FORS analysis, an area of bare paper is used to acquire a background spectrum, which is then subtracted from the spectrum of the colored area. In principle, this gives spectra which should be more directly comparable between standards prepared in the lab and areas on prints.

Figure 1. FORS spectrum of dayflower blue printed on Japanese paper

Figure 4. FORS spectrum of blue drapery in a late 1820s print (MFA 11.26691-2) by Keisai Eisen, corresponding to dayflower

Figure 2. FORS spectrum of indigo printed on Japanese paper

Figure 5. FORS spectrum from blue water in a 1798 print (MFA 11.19657) by Katsushika Hokusai, corresponding to indigo

Figure 3. FORS spectrum of Prussian blue printed on Japanese paper

Figure 6. FORS spectrum from blue drapery in an 1820s print (MFA 21.9254) by Yanagawa Shigenobu I, corresponding to Prussian blue

FORS Reference Spectra

The table below shows reference FORS spectra for many of the Edo period colorants, organic as well as inorganic. Spectra from some mixtures are also shown. Data was acquired over a period of time, and the displays of results are not consistently formatted but are representative of the colorants. It should be stressed that for various reasons, these spectra may not exactly match spectra prepared and analyzed by other researchers and will not necessarily match spectra of the same colorants in prints.

Blues	Greens	Yellows	Reds
Indigo Dayflower Prussian blue Azurite Ultramarine	Orpiment/Indigo Orpiment/Prussian Blue Turmeric/Dayflower Malachite Verdigris	Orpiment Turmeric Pagoda Tree Rice Plant Yellowwood	Madder Safflower Iron Oxide Red Red Lead Vermilion

Analysis

Greens were usually made from a combination of a blue and a yellow colorant, while purples were usually made from a combination of a blue and a red colorant. The blue colorants in these mixtures can usually be determined by FORS analysis. FORS is not usually useful for identifying yellow colorants but can sometimes be useful for the organic reds.