Humankind’s use of ink colouration to communicate images and writing has a long history. Katsushika Hokusai (1760 - 1849) is the Titan of Japanese art, as revered in his homeland as Da Vinci, Van Gogh, and Rembrandt Van Rijn are in the West. Of all his famed masterpieces the ‘Great Wave’ stands out as the ultimate testament to his artistic genius.  

This time could be over now: Researchers from Japan developed a new printing method, which requires exactly zero drops of ink.
It’s smaller than most ants, fruit flies or a pixel – and that´s not even the most fascinating feature of the work from researchers from Kyoto University, Japan. They developed a method to create colourful high-resolution images without using ink: By the use of Organized Microfibrillation they were able to replicate Katsushika Hokusais “The Great Wave” and Jan Vermeers “Girl with a Pearl Earring”.
The human condition demands that we create art. Some 38,000 years before Hokusai picked up his woodblocks and kogatana knives, an inhabitant of the Lubang Jeriji Saléh cave in East Kalimantan, Borneo, Indonesia created the world’s first-known figurative painting when she/he drew a picture of a bull on the wall using ochre. Artists ever since, from the Upper Paleolithic Era to 1800s Japan to the street artists of today, have all shared a common dependency: the need for pigments. 
Until now, that is.  Not only is the ‘Great Wave’ created at Kyoto University the world’s smallest, it is also the first ever printed without use of a pigment. Professor Easan Sivaniah, head of the Pureosity Group at iCeMS, Kyoto University, where the research was developed, explains. 

Crazing is the Key
“Polymers when exposed to stress - a kind of ‘stretching out’ at molecular level - undergo a process called ‘crazing’ in which they form tiny, slender fibers known as fibrils,” he explains. “These fibers cause a powerful visual effect. Crazing is what the bored school kid sees when he repeatedly bends a transparent ruler until the stretched plastic starts to cloud into a kind of opaque white”.
If you´ve ever repeatedly twisted a transparent plastic piece like a ruler, you may have noticed that the stretched plastic begins to turn into an opaque white, rather than staying transparent. These networks of fine cracks, microcavities and hairlike structures called microfibrils tend to form around stress “hot spots” within the polymer structure. This process is known as “crazing” and may be the answer to pigment-less printing.

Colour Control
To fully understand this process, the Kyoto researchers analyzed it by scanning electron microscope snapshots at different times. 

Thus, they were able to document the microstructural changes of the polymer structure. The key, they found, is a periodic structure of porous layers and alternating density to emerge within the plastic. The optical result were standing waves that interfere to create several colours.

By controlling the way microfibrils were formed, the researchers were able to control the scattering of light to create colours from the entire visible spectra. This novel printing method, that is able to create images at resolutions of 14,000 dpi without ink, is called Organized Microfibrillation (OM).

Zoologists have long been familiar with this non-pigment-based color phenomenon, which they term ‘structural color’. It is exactly how nature produces the vivid colors seen in butterfly wings, the spectacular plumage of male peacocks, and other shimmering, iridescent birds. Some of the most spectacular wildlife on the planet is, in fact, devoid of pigmentation and depends upon light interacting with the surface structure for its mesmerizingly beautiful effect.

The OM technology allows an inkless, large-scale color printing process that generates images at resolutions of up to 14000 dpi on a number of flexible and transparent formats. 
This has countless applications, for example, in anti-forgery technology for banknotes. But as Sivaniah is at pains to emphasize, its applications go way beyond conventional printing ideas.

Inkless Printing: What’s Next?
“OM allows us to print porous networks for gases and liquids, making it both breathable and wearable. So, for example in the area of health and well-being, it is possible to incorporate it into a kind of flexible ‘fluid circuit board’ that could sit on your skin, or your contact lenses, to transmit essential biomedical information to the Cloud or directly to your health care professional,” explains Professor Easan Sivaniah, head of the Pureosity Group at iCeMS, Kyoto University, where the research was developed.
OM is flexible technology in both the literal and figurative sense. The Kyoto University researchers have proved the technology works in many commonly used polymers, such as polystyrene and polycarbonate. 
The latter is a widely used plastic in food and medicine packaging, so there is clearly an application in food and drug safety, where security labels can be created much like a watermark to ensure a product has not been opened or sabotaged. 

Masateru Ito, lead author of the paper, published this month in Nature, thinks there is more to come from the basic principles raised by this groundbreaking research. “We have shown that stress can be controlled at the submicron length scales to create controlled structure,” he notes. “However it may be that it can also create controlled functionality. We demonstrated it in polymers, and we also know that metals or ceramics can crack. It is exciting to know if we can similarly manipulate cracks in these materials too.
What do you think: Is OM going to revolutionize the way we print?