Titanium dioxide (TiO2) is the white pigment used to give whiteness and hiding power, also called opacity, to coatings, inks, and plastics. The reason for this is two-fold:
- TiO2 particles of the right size scatter visible light, having wavelength λ ≈ 380 - 700 nm, effectively because TiO2 has a high refractive index
- It is white because it does not absorb visible light
The pigment is expensive, especially when volume prices of systems are used. Most paint and ink companies buy raw materials per weight and sell their products by volume. As TiO2 has a relatively high density, ρ ≈ 4 g/cm3, the raw material contributes substantially to the volume price of a system.