Copal painting medium is an oil paint additive that speeds the drying time of your artwork. This medium increases paint flow and imparts a high gloss and hardness when dried. Only dilute with turpentine or Grumtine, as petroleum based solvents and odorless thinners are not compatible with this product. Details:2.5 fl. oz. (74 mL)Traditional mediumMay cause yellowing or darkening of colors over long periods of timeEnjoy quicker drying times when painting