Alkyds are one class of binder, while another consists of acrylics, vinyls, and other plastics in latex emulsions. Both pigment and binder are applied with the help of a solvent, or liquid, which eventually evaporates. Sprinkled in with these three components are various additives that impart special qualities to the goo. The pigments, binder, and additives comprise the solids content of paint. That's the stuff that counts, because solids are what's left after the solvent disappears.
Manufacturers generally state a coating's solids content as a percentage of both volume and weight.
Pigments constitute anywhere from 30 to 45 percent of paints typically used by residential and commercial painters. Titanium dioxide, a white pigment, is a major factor in paint price. Extender pigments, which include talc, clays, carbonates, and silicas, reinforce and extend titanium dioxide. By themselves, though, they perform poorly as hiding agents. Obviously, it doesn't take a Nobel Prize chemist to figure out how to lower the price of paint.