GOLDEN OPEN Matte Medium Help maximize working time of OPEN Acrylics and can be used to adjust color strength and translucency while maintaining consistency. OPEN Acrylic Medium (Gloss or Matte) will lower paint viscosity to create a more fluid mixture and increase flow. OPEN fluid mediums are also useful for lowering the viscosity of Heavy Body colors and slowing the drying for detail painting using fine brushes.