As in offset litho printing and traditional photographic printing, glossy papers give the highest color density (or Dmax), and therefore the widest color gamut. Photo papers vary in their longevity and their color gamut. Paper suppliers and printer manufacturers often provide color profiles for use with specific inks and printer models. Longevity of inkjet papers is defined according to the stability of certain parameters (for example, fading from exposure to light, change in color balance, ozone resistance, humidity resistance) and depends on the specific combination of inks and paper. For maximum longevity, the paper substrate should be lignin free or cotton-based, or a combination of the two, pH neutral and contain no optical brightening agents in either the substrate or the coatings. Plastic substrates also exist.