XRF analysis of Ukiyo-e prints
Overview
X-ray fluorescence (XRF) spectroscopy is a nondestructive analytical method used to determine the elemental composition of materials. When excited by X-rays, each element emits secondary or fluorescent X-rays that have energies unique to the element. The XRF instrument used in this research, a Bruker Artax micro-XRF spectrometer, cannot detect elements lighter than silicon, thus organic colorants (which mainly consist of carbon, oxygen, and hydrogen) cannot be identified.
For this database, XRF was used to tentatively identify inorganic colorants and metals based on the element(s) detected. For example, if XRF detects the elements arsenic and sulfur in a yellow area, the pigment is most likely to be orpiment (arsenic trisulfide), the most common natural yellow colorant that contains arsenic. While chemical elements can suggest specific pigments, from a scientific point of view other techniques not used in this study are required to identify pigments with certainty (such as Raman spectroscopy or X-ray diffraction). In the case of yellows that contain arsenic, orpiment is the most likely pigment, but there are two other possibilities. In the later part of the Edo Period, a synthetic pigment of the same chemical composition was manufactured, and this artificial pigment cannot be distinguished from the natural mineral by XRF alone. There is also another yellow-colored arsenic sulfide, pararealgar, but to date this compound has not been specifically identified in Japanese prints. Thus, identifications of orpiment, based on detection of arsenic, while probably correct, should be considered tentative.
Other examples:
- Detection of iron in a red or red-brown area likely indicates the presence of red earth or ochre;
- Detection of copper and zinc in a metallic-looking area likely indicates the use of ground brass metal
- Detection of lead in an orange-red area probably indicates red lead, while detection of lead in a white area probably indicates lead white.
XRF Reference Spectra
Below are XRF spectra examples obtained from reference samples of all inorganic colorants that have been historically mentioned as being used in Ukiyo-e printing. Also included are a few other colorants that are know to have been used in painting at that time. We did this to determine which techniques were best qualified to identify the colorants in Japanese prints.
XRF spectrum of Orpiment 
XRF reference spectrum of Iron oxide yellow 
XRF spectrum of Iron oxide red 
XRF spectrum for Brass 
XRF spectrum for Calcite
XRF reference spectrum of Vermilion 
XRF reference spectrum of Red lead 
XRF spectrum of lead white 
XRF spectrum for Tin
