Ultra Blue (21B) - Radiant CONCENTRATED Water Colour is a range of transparent, non-toxic, extremely concentrated, dye-based, non-clogging, intermixable, non-permanent, non-lightfast, non-waterproof, versatile, vivid watercolours, designed for use with brushes, airbrushes and technical pens. Primarily formulated for use in graphic arts work on paper surfaces intended for reproduction (e.g. cartooning, illustration, manga, comics and other graphic arts). Like all aniline dye base colours, they are fugitive when exposed to direct sunlight over time; Dilute with water or blend with another colour to get new colours or graduated tones.