Colour Story: Prussian blue

Prussian blue, an intense blue pigment, has a high tinting strength and produces a range of hues, from the palest tint to a deep blackish-blue. Winsor Blue is part of the Winsor & Newton "Winsor" family of colours, created to replace less reliable colours such as the Prussian blue of the 1700s.

Famous for being among the first modern synthetic pigments ever created, Prussian blue was discovered by chance in 1704 by the Berlin-based colourmaker Johann Jacob Diesbach, when he was creating a red lake pigment to use as a dye, using iron sulphate and potash. On this lucky occasion, the potash was contaminated with impurities in the form of animal oil. Instead of a bright red, Diesbach produced a purple, and when concentrated it became a deep blue pigment. This accidental discovery provided a new alternative to the only permanent blue pigment available, ultramarine (lapiz lazuli), which was extortionately expensive as it was mined in limited amounts in Afghanistan.

By 1710 Prussian blue was being used by many artists in the Prussian court, giving it its name. It spread through Europe in watercolour and oil colour, with artists such as Antoine Watteau and Jean-Baptiste Pater taking it up. It then travelled globally, as far as Japan, where it was used by Hokusai in his woodblock painting The Great Wave off Kanagawa. Since then, Prussian blue has featured in the palettes of artists including Monet, Constable, Gainsborough, Lowry and Picasso in his famous "Blue Period".

Many of these historic paintings using Prussian blue show its tendency to fade and become greyish over time.

Winsor Blue was created as a stable and lightfast version to replace Prussian blue. Launched by Winsor & Newton in 1938, it comes from the phthalocyanine family of colours, which were first chemically synthesised in the late 1920s. Many new synthetic organic pigments were being discovered around this time, but only three were universally accepted for their artist quality in the 1950s: phthalocyanine blue, phthalocyanine green and alizarin crimson.

Winsor Blue has many of the same properties as Prussian blue, including its intense richness of pigment, its transparency and great tinting abilities, but is also completely permanent and lightfast. It mixes very well with other colours and, when thinned, makes a great glaze. It is a deep and intense blue which approaches black in masstone and it is formulated with either a red or green undertone, leading to the variations of Winsor Blue (Red Shade), ideal for mixing purples, and Winsor Blue (Green Shade), which is best for mixing greens.

Watch our masterclass on Prussian Blue below.