Look closely at Hokusai's Great Wave off Kanagawa. The foam on the wave, the snow on Fuji, the clouds: none of that white is printed. The white is bare washi paper showing through, made bright by plant fibres scattering light. A Kyoto University team has now found a way to print white made of structure instead of pigment, and the same process throws off a water-repellent surface as a side effect.

The colour we mine

White is not a design choice. It is infrastructure. The brightness and opacity in paint, paper and plastics come overwhelmingly from one powder, titanium dioxide. The US Geological Survey puts 2025 world production of titanium mineral concentrates at 9.4 million tonnes of ilmenite plus 450,000 tonnes of rutile, and notes that demand tracks TiO2 pigment. In the United States, more than 95 percent of those concentrates went to domestic pigment producers.

White has changed hands before. From ancient Egypt to the early twentieth century the dominant white pigment was lead white, which carried everything from house paint to oil painting until the cumulative neurotoxicity of lead pushed it out. The seat went to titanium dioxide, cheap to make industrially from the middle of the twentieth century.

TiO2 beats the cheaper powders on one number: a refractive index of 2.4, which the iCeMS release calls the highest of any transparent material. The bigger the gap with its surroundings, the harder light reflects off a particle's surface, and the fewer particles you need before a film stops being see-through.

Nature solves the same problem without lead or titanium. The Cyphochilus beetle gets a good white out of scales just 5 to 10 micrometres thick, using a three-dimensional network of chitin fibres. Copy paper needs about 90 micrometres. Peter Vukusic's group reported the effect in Science in 2007.

The same powder, banned in one place and legal in another

In Europe, titanium dioxide is no longer food. Commission Regulation (EU) 2022/63 was adopted on 14 January 2022 and entered into force on 7 February; products made under the old rules could be sold until 7 August 2022. E171 is gone from EU shelves.

Yet Europe's other attempt to pin the substance down collapsed. The harmonised classification of TiO2 as a suspected inhalation carcinogen was annulled by the EU General Court on 23 November 2022, and on 1 August 2025 the Court of Justice dismissed the appeals brought by France and the Commission, letting the annulment stand.

Japan went the other way. Titanium dioxide has been a designated food additive since 1983, used as a white colourant in white chocolate, chewing gum and dragées. Japan's Food Safety Commission finished its assessment in November 2023 and concluded that current knowledge gives no grounds to suggest a safety concern at the amounts used in food.

The ban is narrower than it looks. E171 is titanium dioxide as a food additive; the paint, paper and plastics that take most of the world's supply are untouched, and the classification that would have reached industrial handling is the one the court struck down. The iCeMS release says as much: whether similar rules spread to other countries, or reach pharmaceuticals and industrial products, it calls undecided. So what a Kyoto lab is answering is not a ban already in force but the direction regulation is moving.

The PFAS clock is set more clearly. The universal PFAS restriction proposal reached the European Chemicals Agency on 13 January 2023, filed by five governments: Denmark, Germany, the Netherlands, Norway and Sweden. ECHA published the socio-economic committee's draft opinion on 26 March 2026 and ran a consultation until 25 May 2026. On the timetable as the law firm Covington & Burling reads it, restrictions would not bite before 2029. We have covered the move to fluorine-free materials before, in a membrane from Yamanashi University.

Japan already lost this bet once

Structural colour is not a new idea in Japan, and its commercial record is poor. In 2000, researchers from Teijin, Nissan Motor and Tanaka Kikinzoku published in the Journal of the Society of Fiber Science and Technology on Morphotex, a light-interference fibre modelled on the Morpho butterfly: colour from stacked nanolayers, no dye at all. A quarter of a century later, dye still colours almost everything you wear.

That is the pattern. Structure beats chemistry in the demo and loses on cost and scale. Kobe University's structural-colour nanoparticle ink, which we covered earlier this year, belongs to the same long line of near misses. It is also not a race Japan is running alone. Seprify, a Cambridge spin-out now based in Switzerland and formerly called Impossible Materials, has spent years turning the beetle's trick into a cellulose powder called SilvaAlba. FoodNavigator reported in March 2026 that the company had moved from pilot validation to procurement-ready industrial supply, backed by a 13.4 million euro Series A whose investors include Inter IKEA Group. Seprify's is a different kind of product: SilvaAlba is still a powder you add to something, while the Kyoto method makes the white out of the material itself and prints it. The two accounts also do not quite fit. The iCeMS release says earlier biomimetic structural-white work never reached a stable pigment, which sits oddly beside a company saying it has procurement-ready supply.

Taiki Yanagishima, the Tokyo Metropolitan University associate professor on the team, put the problem plainly in the announcement: the hardest part of biomimetics is getting a nature-inspired design onto a "scale and cost" that can stand against the materials already in use.

What is different this time

The method, developed in Easan Sivaniah's lab at Kyoto University's iCeMS, is called Deep Foam Photolithography, DFP for short.

Start with an ordinary transparent polymer film with a photo-crosslinker mixed in. Shine UV-A light through it. Radicals form, and some polymer chains are cut while others cross-link, all the way through the depth of the film rather than only at the surface. Then soak the film in a weak solvent. The solvent permeates, the cut fragments swell, pores open, and pores collapse in a controlled way. What is left is a foam whose countless air-polymer interfaces scatter light in every direction. That scattering is the white. Push the conditions further and the foam walls thin past their limit and burst, squeezing out solvent and leaving the polymer to precipitate. In a crystalline polymer it sets into something the team likens to an opened flower, and that is what gives the lotus-like super-hydrophobicity.

Because light draws the structure, this is a printing process. The team reports about 20,000 dots per inch, which puts the dots roughly 1.3 micrometres apart.

It needs no new specialty chemical, the iCeMS announcement says, and the release lists polystyrene, polycarbonate, polysulfone, cellulose acetate, PMMA and PET, all off the shelf. It works on fibres and fabric as well as film, demonstrated with textile researchers at Donghua University in Shanghai. Claudia Rosa, a co-author who came to Kyoto University after 20 years of filmmaking in Milan, wrote in a Nature Research Communities post that within a year the team carried the printing from centimetres to metres, a ten-thousand-fold increase in area.

Sivaniah's group has moved research into business before, with a CO2-reduction startup called OOYOO. The release says the long-term plan is a startup built on this technology, working with large ink makers and printing companies.

Kyoto artisans, and the numbers nobody has yet

The work with Kyoto craftspeople, as the release describes it, means folding screens, lamps and washi papermaking, plus a parasol that is both brilliantly white and water-repellent. And oshiroi, the white face paint of geisha and stage performers, which carries its own history: the old formulation contained lead and was banned in 1934 over skin toxicity. The question is whether a version with no metal in it at all can be made.

The open questions are the ones that killed Morphotex. 3,000 joules per square centimetre at the top of the exposure range is a great deal of light, and energy per square metre is what decides whether a process competes on price. Durability, mass-production cost and head-to-head comparison against existing products all remain untested, as Tokyo Hodo Shimbun noted in its coverage. And "world's highest level of white" is the release's headline, while the body of that same release says the white is on a par with titanium dioxide. The Nature abstract makes no superlative claim either. The work was supported by JSPS KAKENHI grant 23H05468 and the Kyoto University-Mitsubishi Corporation Startup Catapult.

If you are reading this in the EU, the white in your sweets quietly changed in 2022 and you almost certainly never noticed. In Japan it did not change at all. How much of what we call colour is chemistry we have agreed not to think about? What is the white in your country made of, and would you notice if it were swapped for a pocket of air?

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