Portland Grey Medium: An interesting alternative to mixing with white, the Portland Greys can mute the high key tints of the modern colors for more natural looking mixtures. Formulated using the Munsell System for painters who work with value. Pigment: Titanium dioxide, zinc oxide, bone black (PW 6, PW 4, PBk 9), Vehicle: Alkali refined linseed oil Lightfastness I, VALUE 6, OPAQUE.