COLOUR LIBRARY · MECHANISM
Structural colour
Most colour is a pigment absorbing part of the spectrum. Structural colour is different: nothing is absorbed, and the colour comes from the geometry of the surface itself. It is the reason a morpho butterfly’s blue does not fade, and the reason the effects built on it are so hard to buy.
1 · Colour without a colourant
When a surface is structured at a scale comparable to the wavelength of visible light — roughly a few hundred nanometres — light interacts with the structure rather than simply bouncing off it. Reflections from repeating layers or features interfere with one another, reinforcing some wavelengths and cancelling others. The eye receives a colour that no pigment in the material produced.
Because no dye or pigment is involved, there is nothing for ultraviolet light to break down. Structural colour does not fade in the way pigment colour does; it only changes if the structure itself is damaged or contaminated. The trade-off is that it is almost always angle-dependent, since the geometry that produces it is directional.
2 · Where it occurs in nature
Nature uses it constantly. The blue of a morpho butterfly’s wing comes from ridged scales, not blue pigment — the mechanism set out in Vukusic & Sambles, “Photonic structures in biology”, Nature 424 (2003). Peacock feathers, beetle shells, the inside of a shell and the blue of some bird feathers all work this way. Very few animals produce genuine blue pigment; most apparent blue in nature is structural, which is a reasonable clue to how difficult blue pigments have historically been — a theme the rare colour index follows.
3 · Where it appears in coatings
The commercially established form is the interference pigment: a transparent platelet carrying a metal oxide layer of controlled thickness, so that reflections from the top and bottom of the layer interfere. That is a thin-film structure, and it is the mechanism behind pearlescent and colour-shift finishes. Layer thickness sets the colour, which is why these pigments are specified by the travel between two hues rather than by one.
Beyond that sit more elaborate approaches — multilayer flakes, engineered particle arrays and photonic structures — which produce more saturated and more strongly shifting effects. These are where the well-known research finishes live. They are also where the difference between a demonstrated result and a purchasable product is widest, and some of the most asked-about examples are manufacturer processes rather than materials anyone can buy.
4 · Why it is hard to specify and buy
Three practical problems. First, a single colour value cannot describe it, so any specification must state the viewing geometry or the two hues the colour travels between. Second, the effect depends on what is underneath: interference platelets are partly transparent, so the ground coat is part of the specification, not a detail. Third, the structure is fragile in the sense that contamination, poor dispersion or the wrong film build can flatten the effect entirely.
Commercially, the field runs from ordinary interference pigments available through normal channels to proprietary processes that cannot be bought at all. Nothing on this page should be read as a statement that a particular structural-colour finish is obtainable. If one matters to a project, the useful question is what appearance you actually need, because there is often a route to it that does not depend on the exact material that made the headlines.
What BADAR can do with a structural-colour requirement is narrower than the subject suggests, and worth stating plainly. Ordinary interference and colour-shift pigments are trade material: send the binder system, the application method, the quantity and the destination, and we investigate grades against it. Named proprietary finishes are a different question, and the answer is frequently that nothing is purchasable — we would rather reach that early than keep an enquiry open. Because these materials are specified by behaviour rather than by a colour value, the first thing we do is turn your description into something a supplier can quote.
Practical expectations. Minimum order is set by the manufacturer and the route for the grade, not by us, and evaluation quantities are quoted separately where a manufacturer offers them. Lead time depends on where the answer sits: a current pigment through a known channel is quick, while a made-to-order effect runs on a production schedule we quote as given. We publish no prices, because grade, quantity, route and destination all move the figure. Anything supplied arrives with the manufacturer’s technical data sheet — the authority for dosage, particle size and orientation — and its safety data sheet; pigments placed on the EU market fall under REACH, and classification under CLP follows the chemistry rather than the appearance.
FROM LEARNING TO SOURCING
Describe the effect and the object rather than naming a famous finish, and we will tell you what is commercially obtainable for it — including when the answer is nothing.