Ultramarine Red Violet - 36H - Hydrus Fine Art Watercolor is a range of lightfast, transparent, brilliant, acid free, archival grade, pigment based, non-clogging, intermixable, non-toxic, lightfast, high quality artist watercolours. Designed specifically for use with technical pens, fountain pens, calligraphy pens, and drawing pens. Ideal for design and illustration.