Hokusai is famous for his prints: his wave has travelled the centuries to become a popular icon, as well as his view of the Mt Fuji.
But what technique did he used? Wood-block printing, or, in Japanese, Ukiyo-e. This is a very old technique, used as far as Ancient Egypt, China, or Syria, that consists in two parts: first engraving woodblocks with the image, then using paints to transpose the image from the wood to the surface, paper or fabric.
Typically, paint is deposited on the parts of the woodblock that are the most elevated. In some cases, some kind of viscous glue is added as well. Then, rice paper is placed onto the woodblock, making sure it is well positioned. Rice paper has two side: a smooth and a rough side. The print is made on the smooth part.
To make the paint adhere to the paper, a flat piece is used to press the paper on the wood.
This is done for one colour, and the process is repeated for the other colours, each time using a different woodblock. See below the steps for reproducing a drawing from Toshusai (18th century), representing the portrait of an actor.
Similarly to many art pieces, Ukiyo-e have still many things to reveal. Collectors, artists, scientists and historian are resolve all of their mysteries. Studying the pigments, new non-invasive techniques are developed, and the results used to reconstruct the history of this period in Japan, such as the use of amorphous arsenic sulfide for golden colours [1-3]. These spectroscopy methods can then also be used in criminology.
New in the scene of artwork studying, artificial intelligence and neuronal networks can be developed and applied to read scriptures. One example are the Mongolian encyclopedia Kanjur, written from woodblocks .
 Characterization of Yellow and Red Natural Organic Colorants on Japanese Woodblock Prints by EEM Fluorescence Spectroscopy, M. Derrick, R. Newman, J. Wright, Journal of the American Institute for Conservation, 2017.
 Evidence of early amorphous arsenic sulfide production and use in Edo period Japanese woodblock prints by Hokusai and Kunisada, M. Vermeulen, M. Leona, Herit sci, 2019.
 Red and blue colours on 18th-19th century Japanese woodblock prints: In situ analyses by spectrofluorimetry and complementary non-invasive spectroscopic methods, A. Mounier, G. Le Bourdon, et al. Microchemical Journal, 2018.
 A holistic recognition approach for woodblock-print Mongolian words based on convolutional neural network, H. Wei, G. Gao, IEEE, 2019.