Artist Material – Prussian Blue Pigment

In the scientific analysis of art materials is important to understand as much as possible about potential materials used by an artist. For centuries artist used natural materials such as minerals, clays, resins, and plant extracts to give them the colors necessary for painting.  However, many natural materials do not withstand the test of time and fade on exposure to light and heat. The search for improved materials for paintings and coatings continues to this day, but a discovery made 300 years ago produced a pigment which was widely used in popular well into the 20th century.

Prussian blue is often referred to as the first modern pigment with its discovery in 1704 by a color maker named Diesbach in Berlin, Germany. The pigment was actually discovered by accident when Diesbach ran out of some of his raw materials it is using to produce a red pigment called Florentine Lake.  When he used an alkali which was from an animal source, the reaction product was a strong blue material rather than the expected red.  This serendipitous discovery milori-blue resulted in a very popular pigment which was quickly put into use in Europe and then America and Asia.  The pigment Prussian blue has the formula Fe4III [FeII(CN)6]3 ·xH2O   and has the chemical name hydrated iron hexacyanoferrate complex.  In the early years following its discovery was often named in association with the place where it was being produced such as Paris blue, Hamburg blue, and Erlangen blue.  On mixing with other pigments such as barium sulfate or alumina, was named Brunswick blue and Antwerp blue.

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The pigment was used in paints as well as printing and has been used by a number of notable artists.  Among some of the first artists to take advantage of this new pigment beginning in the early 1700s were Dutch painter Adriaen van der Werff, French painter Antoine Watteau and Italian painter Canaletto.  In England, artists such as William Blake and John Constable also used the pigment blended with different yellow pigments to produce greens.  In America, John Audubon use the pigment in his engravings in The Birds of America.  Winslow Homer also used Prussian blue in watercolor paints.  A number of Impressionist and Post-Impressionist paintings have also taken advantage of the pigment including works by artists Paul Cézanne, Georges Seurat, Edgar Dégas, Claude Monet and Vincent van Gogh.  Van Gogh’s painting Starry Night is a notable painting that makes of the use of this pigment.

From a material analysis point of view, the characterization of this pigment can be accomplished by examination with a microscope and microchemical tests. Prussian blue is very sensitive to alkali and will turn a brown color, but it is insensitive to acids.  It does not have a typical pigment particle morphology and can be differentiated from materials such as ultramarine, lapis lazuli, azurite, and smalt.  When examined with an FT-IR microscope, the resulting spectrum has a very characteristic band related to the presence of the cyano (C≡N) groups around 2100 cm–¹.  This FT-IR band is also sensitive to minor variations of the chemistry and can shift slightly based on pH, hydration, and oxidation state of the
iron in the pigment.  When blended with some pigments Prussian blue could become discolored as the iron atoms in the pigment were interchanged with metal atoms from the other pigment such as lead from lead white.  Although Prussian blue is still available as a pigment, phthalocyanine blue (discovered in the 1930s) began to replace Prussian blue in many applications both in art materials and in industrial applications through the 20th century.