Ultramarine ash ∨ ashes Meaning, Definition & Usage

Definitions
  1. (Paint.), a pigment which is the residuum of lapis lazuli after the ultramarine has been extracted. It was used by the old masters as a middle or neutral tint for flesh, skies, and draperies, being of a purer and tenderer gray that produced by the mixture of more positive colors. Fairholt.

Webster 1913