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 the three common blues are shown below, along with spectra of each blue from a print. The paper used in the 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.

FORS spectrum of Dayflower reference

Pt 5: Printed Keisai Eisen, 11.26691-2

FORS spectrum of Indigo reference

Pt 5: Printed Keisai Eisen, 11.26691-2

FORS spectrum of Prussian blue reference

Pt 3: Printed Yanagawa Shigenobu I, 21.9254

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 also will not necessarily match spectra of the same colorants in prints.

FORS Reference Spectra

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.