Prussian Blue is a deep blue colour. It was made by German chemist Diesbach around 1704 making it the first synthetic blue pigment. It quickly gained favour as an alternative to genuine Ultramarine.

Cotman Watercolours use fine art pigments with reduced pigment load than the Professional Watercolour range, making them an accessible choice while still uncompromising on quality. Rated AA and A for Excellent and Good lightfastness, Cotman Watercolour gives artist the reassurance expected from a quality watercolour range.