Raman and X-ray fluorescence spectroscopies reveal the mysteries behind ancient Japanese art form

Kabuki actors, sumo wrestlers and female beauties. These, along with scenes from history and folk tales, travel scenes and landscapes, and flora and fauna are featured in Ukiyo-e, a category of Japanese art popular between the 17^th and 19^th centuries.

One art reproduction specialist recognized he had to understand the pigments and dyes used in the original works to properly reproduct the art as a copy of the original with the same quality. So he turned to science, and HORIBA spectroscopic instruments to determine its makeup.

Ukiyo-e translates to “pictures of the floating world,” and refers to Japanese paintings and woodblock prints that originally depicted the cities' pleasure districts during the Edo Period (1603 – 1868), the final period of traditional Japan. The art form featured woodblock carved printing and painting.

Its narratives show the leisure activities and climate of the era, as well as representing the Japanese aesthetics of beauty, poetry, nature, spirituality, and love.

Yuya Shimoi of Shimoi Woodblock Printing Co., Ltd. in Kamakura, just south of Tokyo, asked HORIBA’s Hakaru LAB in Tokyo for help charactering Ukiyo-e paints. The HORIBA Group has 17 analytical centers in 10 countries to meet the ground-breaking analysis needs of each region. 

“Reproduction” is about how to make something of the same quality as the original,” Mr. Shimoi said. “Here is a ‘reprint’ with a similar expression, and many reprints are on the market in the world of Ukiyo-e, but the tendency of Ukiyo-e reprints is as a higher grade as works of art and ornaments required in that era. There is a part that has been made with the aim of being expensive. Therefore, in the extreme, some paintings and compositions are Ukiyo-e, but the colors are boldly changed according to the lifestyle and taste of modern people. As a result, with special exceptions, the material is often completely different from the original.”

In Ukiyo-e, reproduction specialist first carve the outline, then look at the original picture and perform "color separation" to color-code it when making a plate. They try to address what and how many color are used. This color separation is a task that can be done with the naked eye as long as the color has not faded much. This is because you can compare it with a well-preserved work in an art book, or even if the color has faded, you can select the part that has faded in the same way from the figure. However, what is needed in the process of rubbing each color plate is the determination of the color of the paint itself.

While almost no information having been handed down on these processes, it’s not possible to accurately determine the material of the paint from the visible information alone.

“Therefore, I decided to incorporate scientific precision analysis in order to find out the essence that I wanted to achieve,” he said, “how to make the same quality. In addition, there are still many mysteries about the paints of Ukiyo-e in the Edo period, and I felt that it was necessary to analyze the paints of that time not only for making works but also from the viewpoint of studying Ukiyo-e in Edo.”

Mr. Shimoi usually makes color assumptions by searching the literature. For example, although it is said that there were several types of "yellow" paint, these had not been detected in previous surveys, or in the literature.

“There is overwhelmingly little clear data on how it actually happened. The paints used vary depending on the author and the times, and if you include the transition of what kind of person they got after that, you really don't know what kind of material they are colored with.” he said.

Therefore, Mr. Shimoi thought it was necessary to analyze the paints precisely using the actual Ukiyo-e original drawings.

“I searched a lot of companies that analyze and measure, but I could not find any company other than HORIBA that analyzes cultural properties and can even analyze dyes such as Ukiyo-e,” he said. “It's exciting just to imagine that each color of paint is related to the background of the times. I feel very grateful to be able to witness such a thorough analysis.”

Mr. Shimoi brought in a work called "Tokaido 53rd Nouchi Mizuguchi Choemon" (Kaei 5/1852), by Utagawa Toyokuni, extremely popular in the latter half of the Edo period. The third generation of Kunisada. Against the backdrop of the famous "Fifty-three Stations of the Tokaido" by Hiroshige Utagawa, one of a series in which popular actors at that time were arranged in the style of stories and customs associated with each post.

Ukiyo-e paints include pigments and dyes. Pigments represented by mineral paints are also used in Japanese paintings and Western paintings, while plant-based dyes such as turmeric and safflower are especially unique to Ukiyo-e works of the Edo period.Mineral-based pigments can be analyzed for elements by X-ray fluorescence analysis, and plant-based dyes consisting of organic compounds can be identified by Raman analysis. Therefore, HORIBA used a method to identify the materials from the obtained elemental information and molecular structure by using a HORIBA XGT-5200 X-ray Analytical Microscope and a HORIBA LabRAM HR Evolution Confocal Raman Microscope respectively.

Once primary X-Rays irradiate a substance, the substance releases characteristic X-ray signals, called fluorescent X-rays, corresponding to the elemental composition of the substance. This analytical technique is a non-destructive approach and it doesn’t need any special sample preparation and special sample environment condition. Therefore, it is widely used for precious sample analysis such as paintings and archeological specimen.

HORIBA’s micro-XRFs are energy-dispersive X-ray fluorescence microscopes, which are equipped with microprobes and a motorized stage. These features make it possible to carry out elemental analysis in microscopic level even on a large sample non-destructively. Especially, the XGT-5200 open chamber model*, which we used in this project, doesn’t have chamber door, and it allows a stage scan within 100 mm x 100 mm area on a large sample without limitation of chamber capacity.

*This product has been discontinued, and  its features have been integrated into a new model XGT-9000SL, a super large chamber model with superior speed and flexibility.

When a substance is irradiated with light, Raman scattered light with a wavelength different from that of the incident light is emitted due to the interaction between the light and the substance. The Raman spectrometer is a device that disperses the Raman scattered light and analyzes the type and molecular structure of the substance from the obtained Raman spectrum. Since Raman scattered light is much weaker than incident light, the performance of parts such as light sources and spectroscopes and the optical design greatly affect the performance of the equipment.

HORIBA's Raman spectrometers are equipped with the highest-end grating backed by the technology of Joban Yvon (currently HORIBA France), which is a pioneer in the field of spectroscopy, as a core part.

Since it does not touch the sample directly, it is a "non-contact / non-destructive" analysis method, like X-ray fluorescence analysis, but since it irradiates a monochromatic laser, specially colored samples tend to absorb light. The sample may be damaged depending on the conditions, so the analysis was performed carefully.

X-ray fluorescence analysis provides us elemental information of a sample, and it is an effective way to identify inorganic compounds of painting materials. Raman analysis provides molecular information of a sample, and it is effective in identifying organic compounds of paint materials. For example, we know "Bello indigo (C18Fe7N18): blue color" and "Bengala (Fe2O3): red color". Once we can detect Iron (Fe) in an unknown paint areas by X-ray fluorescence analysis, we can narrow down the candidates of the unknown paint by identifying the molecular structure of the iron containing substance using Raman analysis. Thus, these two microscopic techniques are complementary to each other and the combination of the two techniques is helpful in identifing unknown substances.

“I tried color separation by myself and focused on the points that were particularly difficult to distinguish,” Mr. Shimoi said. “Although I had made various predictions, the result was that I was disappointed at many points. For example, "white lead", a white paint made from lead, was used more widely than expected. It was mentioned in the literature that white lead is used in combination with other colors, but in this work, white lead was detected in most of the sky and kimono.”

“There is also "gofun" (powder) made from oyster shells as a white color, but it has not been clarified how lead white and white gofun were used properly. Is it arbitrary by the author at that time, is there some regularity, or is there a historical background? Similarly, "glue", which was added not as a color but for the purpose of preventing the dispersant when the pigment is dissolved in water and the peeling and separation of the paint after drying, was also detected part. I found some mysterious points such as the presence or absence of regularity in the other parts.”

He found some materials that he never expected. For example, the analysis detected “’Titanium white” on the lips. Not only is this not mentioned in the literature, but it is a color that did not exist in the Edo period in the first place, so it is possible that it was painted with complementary colors in later years.

“In this way, there were some results that were far from what was expected, which could not be discerned with the naked eye,” he said. “There are some parts where the mystery has deepened, but I hope to find some answers by accumulating more analysis points in the future.”

But did the analysis affect the work’s colors in the reproduction?

“There was such a discovery,” he said. “Originally, I thought that the color of the outer corner of the eye was the fading of the dye. I thought that safflower (red), which is used in red, tends to turn brown due to aging. However, it turned out to be Bengala (brownish orange) in reality, and it turned out that it was brown from the beginning.”

“Similarly, Bengala was detected in other red parts, which means that there was more red than what was expected. Without this analytical result, it would have been rubbed in red with a slightly used amount of red iron added, based on red as originally expected. The outer corners of the eyes give a particularly strong impression of the whole, so I think that the image of the finished work was quite different.”

Will such a scientific approach help reproduct Ukiyo-e in as he moves forward?

“From this result, we can see that the color of the finished product may change drastically depending on whether or not it is analyzed, and "analysis" is a very effective means for reproduction,” Mr. Shimoi said. “I feel that. This analysis alone may not be clear and the mystery may have deepened, but it is also very good for studying Ukiyo-e in the Edo period, taking into account factors such as the background of the times and the habits and techniques of each master. It was a discovery.”

“In the future, I would like to proceed with research along with the production of works while accumulating data by increasing the score of this scientific analysis.”

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