First, the type and content of harmful impurities in titanium dioxide, even if the content is very small, will have a significant impact on the whiteness, such as iron, chromium, cobalt, antimony, copper, manganese, vanadium, lead and so on. The harmful effects of impurities are not only due to the coloration of the impurities themselves, but also due to the existence of impurity ions, especially heavy metal ions, which cause the titanium crystal lattice curve to twist and deform and lose its symmetry. Rutile titanium dioxide is more sensitive to the effects of impurities, such as iron oxide in the rutile titanium dioxide content of more than 0.003%, it will show color, and anatase titanium dioxide content of more than 0.009% will occur Color reaction.

Second, the shape, size and size distribution of titanium dioxide particles will have an effect on the whiteness. The particle shape of titanium dioxide requires a smooth profile without edges and corners because the angular surface weakens the reflection of light. The particle size should be controlled between 0.2 and 0.4 μm. That is equivalent to half of the wavelength range of visible light (0.4 ~ 0.7μm), so as to obtain high light scattering ability, making its color appear whiter. When the particle size is less than 0.1 μm, the crystal is transparent; when the particle size is too large, even if a small amount (0.1% to 2%) of large particles having a particle size of 0.5 μm or more is contained in the product, the particles will be reduced in light. Scattering power can have a very detrimental effect on pigment properties. For the particle size distribution, it is required to be uniform and the distribution band should be narrow.

Third, the refractive index of titanium dioxide is the highest among white pigments. Therefore, in theory, its hiding power is also the highest. However, the titanium dioxide particle size, particle structure and degree of dispersion affect its hiding power. In the range larger than the half wavelength of visible light, the finer the particle size, the greater the dispersibility, and the greater the hiding power. But it has a certain limit. When the average particle diameter is 0.2 μm, the hiding power is the greatest, and when the average particle diameter is less than half of the visible light wavelength, the hiding power is decreased due to the transparency of the crystal to the light. Therefore, it is not good if the particle size is too large or too small.