Copal painting medium is an oil paint additive that speeds drying time. This medium increases paint flow and imparts a high gloss and hardness when dried. Best used for arisan painting versus fine art application, Copal painting medium may cause yellowing or darkening of colors over long periods of time. Only dilute with turpentine or Grumtine as petroleum based solvents and odorless thinners are not compatible with this product. Made in the USA.