We know that iron is silvery white and iron powder is black, because iron powder has a small surface area and no fixed geometry, and the light that iron powder does not absorb is diffuse, so it is black because there is less visible light that can enter the human eye. In practice, the damping motion of electrons in particles, the existence of lattice defects and inelastic collisions will weaken the vibration frequency of electrons. At the same time, the motion of the electron itself will also produce damping dipoles around the nucleus. These effects will weaken the vibration of electrons, and in order to maintain their own movement, electrons must absorb energy. They only absorb waves of their own frequencies, and this selective absorption leads to the appearance of colors of nanoparticles. Particles of different sizes and shapes have different damping phenomena. Generally speaking, the damping phenomenon of small particles is obvious, so the vibration frequency of small particles is less than that of large particles, and they also absorb long-wave light and reflect short-wave light. With the increase of particles, the wavelength of light wave absorbed by them becomes shorter, which is called red shift. However, the powder of non-metallic diamond does not seem to be black. In modern technology, diamond micropowder refers to diamond particles with a particle size less than 36/54 microns, including single crystal diamond micropowder and polycrystalline diamond micropowder. Single crystal diamond micro-powder is made of artificial diamond single crystal abrasive particles, which are crushed and shaped and made by special technology. Polycrystalline diamond micropowder is made of graphite by a unique directional blasting method. The shock wave of directional blasting of high-energy explosives makes the metal flyer fly faster and hit the graphite flake, which leads to the transformation of graphite into polycrystalline diamond. Its structure is very similar to natural diamond, which is formed by unsaturated bonds and has good toughness. (Source Baidu Encyclopedia) Diamond particles of this diameter are not dispersed to appear black, so it is known that the truly black diamond powder should be fine to nanometer level. It is impossible for the ancients to make diamonds below micron level ..... Nanoparticles won't scratch tissues. Well, now we can rule out the possibility that the diamond powder itself is black. If the black color of diamond powder in the above picture is an impurity, what should I do if the diameter of diamond powder is in micron level? Can't let people taste its existence. Not to mention the preparation method, probably the same as eating fine sand, the wear force will not be great.