First of all the three main components of paint, the pigment, the solvent and the binder, are mixed, but not dissolved. Then you spread the paint on the surface, thanks to the liquidity of the solvent. Over time, depending on the substances used, the solvent dries. Subsequently, the monomer molecules are able to bond to form a polymer chain of whatever liquid polymer was used. During this phase the pigments remain trapped in the bonds and this forms the hard, dry surface