In addition to self-luminous colors, the colors in life mainly include pigment colors (such as the color of flowers), as well as structural colors (such as the color of peacock feathers).
Let's first look at the color of the pigment. As we all know, the white light we usually see is actually composed of many colors, and the following figure shows Newton's experiment of using prisms to decompose sunlight into multiple colors.
Newton used prisms to break down sunlight into multiple colors of light
As I said earlier, most of the color of flowers is caused by pigments. When white light shines on a yellow flower, except for yellow light, all other colors of light are absorbed by the flower, and only yellow light is reflected into our eyes, so we see that the flower is yellow. And no matter from which angle you look at this yellow flower, its color will not change, which is the characteristic of pigment color.
The pigment color of the flowers
For structural colors, the most common example in life is probably a disc: looking at a disc from a different angle, we can see different colors. This color that changes with the angle of observation is called rainbow color.
The iridescent color of the disc
By placing the disc under the microscope, we can see the tiny structures regularly arranged on the surface of the disc, which are the data recorded on the disc. It is precisely because of these tiny structures that the structural color of the disc is caused.
50x disc under the mirror
But not all structural colors are rainbow colors. For example, the color of the eastern blue feathers also comes from the structural color, but does not change with the viewing angle. This blue color is caused by light scattering by irregular microstructures.
The disordered microstructure of the Eastern Blue Plover and its blue feathers
Let's take a closer look at the structural colors of nature. The first structural color generation mechanism is a single-film interference, where the thickness of the film is required to be very thin. An example often seen in life is the color of the oil film on the water. Different colors of light interfere with different angles of incidence and oil films of different thicknesses, resulting in a rich color of oil films.
Schematic diagram of monolayer thin film interference (left) and thin film interference formed by oil in Metasequoia seeds on water surface (right)
Many insects also have thin wings that can interfere with the membrane, such as the two species of insects in the picture. The next time you see small winged insects, look for beautiful rainbow colors on their wings.
Beautiful rainbow color on insect wings
There is a butterfly called the Green Phoenix Butterfly, which has beautiful green spots on its wings and transparent scales on it. These scales also act as membrane interference, making the green spots more vivid in color. Looking at the area of the red frame with a microscope, the green luster produced by the transparent scales becomes more vivid.
Blue butterflies with transparent scales under the microscope
The wings of the butterfly under the microscope correspond to the red-boxed area in the figure above
Another mechanism for producing structural colors is that light interferes in a multilayer film, which is alternately superimposed by two substances with different refractive indices.
Schematic diagram of multilayer thin film interference
For most metallic beetles, their shells contain a multilayer film structure. Using an electron microscope to observe the cross-section of the Gidding's shell, you can see the micro-multilayer structure.
Electron microscopy picture of a section of the gidding insect shell with metallic luster (left) (right)
In addition, the shiny blue ribbon on the neon carp is also because of the multi-layer structure in the cell, the lower right of the figure below is a schematic diagram of step-by-step enlargement, and the rightmost schematic diagram shows the multi-layer structure in the cell.
The shiny blue bands of neon lipid carp are caused by a multilayer membrane in the cells
There is also a structural color caused by photonic crystals, the so-called photonic crystals are microscopic structures formed by the periodic arrangement of two substances with different refractive indexes.
The structural color of peacock feathers comes from the photon crystal structure inside the feathers. On the right, an electron microscope picture of the cross-section of the peacock feather twig can be seen, and the periodic structure, i.e. the photon crystal, can be seen.
Peacock open screen (left) feather section under electron microscope (right)
In addition, the tail feathers of the magpie also have rainbow colors, which are also caused by photon crystals, and from the electron microscope photos of the section of the right feather twig, the columnar stomata of the periodic configuration on the feather can be seen.
Tail feather section of the black-billed magpie (left) electron microscope (right)
Many biochromatics are also associated with structural colors. For example, the leopard chameleon's body turns yellow in a relaxed state and turns yellow under pressure. The reason for this change is that the photonic crystals in the skin change from a denser arrangement to a looser arrangement.
The principle of color change of leopard chameleons
Structure color technology at present, is more and more application in product design, now product designers in addition to pay attention to the traditional color, materials, processes of the product, but also pay more attention to the decorative texture effect of product appearance.
This is because consumers not only meet the functional requirements, but also put forward higher expectations for the beauty and temperament of the structural color of the product.
The structural color of the product can express the pattern of the pattern, texture effect, light and shadow change and so on. But now the Suzhou Impression team has created a micro-nano structure color by carrying forward and extending the holographic technology they are good at, which does not require printing and other processes, is more environmentally friendly, and can also show richer effects from dynamic and color.
In the future, the differentiation of industry products will be smaller and smaller, but consumers' requirements for the texture and appearance of products are increasing, how to achieve differences in similar products, only from the performance of products has been difficult to have a big breakthrough, and need to consume a lot of financial and labor costs of enterprises. At this time, good surface decoration texture and continuous innovation and optimization of CMF are of great benefit to enterprises to continuously launch new products and attract consumers, which is also a major trend in future product design.