There are a huge variety of coating colors and finishes for many different applications, and all of them have one thing in common - their properties are dependent on the size and the mass- or volume-weighted size distribution of the particles used in their ingredients. The average particle size of coating ingredients has decreased over the years from around 0.5 µm to 0.2 µm, in part because of improvements in technology. In addition, there has been a dramatic shift away from solvent-based coatings to water-based coatings in an effort to reduce VOC emissions. The combined result of this has meant a lot of research to find new raw materials and ways to stabilize the rheology of the coatings and maintain their performance. For example, cellulosic thickeners were favored when solvent-based coatings dominated the market, but they were found to decline in performance in water-based systems, and associative thickeners were subsequently developed to achieve the desired rheology.
Having the correct particle size is obviously crucial for reproducible characteristics, and this can be illustrated with one of the most common white pigments, titanium dioxide (TiO2). TiO2 provides opacity and whiteness in, for example, architectural coatings by scattering visible light, and it has one of the highest refractive indices of any common compound.