Prussian Blue

Prussian blue, discovered in the early 18th century, is one of the first synthetic pigments widely used by artists. i Known for its rich, deep blue hue, it quickly became a dominant colorant in painters’ palettes and has since been regarded as the first modern pigment.ii Its chemical structure, based on iron (III) ferrocyanide (C₁₈Fe₇N₁₈) complexes, revolutionized the production of blue pigments, offering an alternative to expensive and labor-intensive natural blues like ultramarine. 

Historical Discovery and Early Use 

The discovery of Prussian blue is attributed to the German dye-maker Johann Jacob Diesbach around 1704. While working in Berlin, Diesbach accidentally synthesized the pigment while attempting to create a red dye. The process involved using potash and animal oil that had been contaminated with iron cyanide, leading to an unexpected brilliant blue pigment instead of the desired red.iii 

Prussian blue became an instant success due to its vibrant color, which offered an affordable alternative to traditional blues like ultramarine, derived from lapis lazuli. Its popularity quickly spread across Europe, with its production reaching France and England by 1720s.iv v Artists, printers, and manufacturers adopted it for use in oil paintings, watercolors, and printing inks. 

Chemical Composition and Variants 

Chemically, Prussian blue is a complex iron hexacyanoferrate compound, generally represented by the formula Fe₄[Fe(CN)₆]₃·xH₂O. The pigment contains iron in two oxidation states—Fe(III) and Fe(II)—which contribute to its characteristic intense blue color. The pigment is colloidal in nature, and different formulations may contain potassium, sodium, or ammonium ions, which slightly alter its appearance or working properties.vi 

Various forms of Prussian blue, such as Milori blue and Chinese blue, differ in particle size and tone. Milori blue is less jet blue and more reddish, while Chinese blue has a greenish undertone. These variations arise from differences in the preparation processes, which may involve varying potassium, ferric ions, and oxidation states during synthesis.vii 

Historical and Artistic Applications 

Artists widely adopted Prussian blue due to its intense color and relative affordability. It was used extensively in European easel paintings, replacing more costly blues. Notable artists, including J.M.W. Turner and Vincent van Gogh, employed Prussian blue to create vivid skies and backgrounds in their works.viii The pigment was also favored in the production of wallpapers, textiles, and prints, particularly in Japan during the Edo period, where it became a preferred choice for woodblock prints.ix 

In addition to fine art, Prussian blue played a significant role in industrial applications. It was used in the production of blueprints, a process known as cyanotype, discovered in 1842 by John Herschel. In this method, light-sensitive paper treated with a solution of Prussian blue was used to create photographic prints. The pigment was also a primary color in house paints, printing inks, and cosmetics.x  

Properties and Stability 

Prussian blue has strong tinting power and excellent opacity, making it suitable for both transparent and opaque applications. However, it is also known for its sensitivity to light and chemical interactions. When mixed with certain pigments, especially those containing lead or zinc, Prussian blue may experience discoloration or degradation over time. It can also lose color when exposed to strong alkalis or acidic conditions.xi 

References

 i Barbara Hepburn Berrie, ed., “7 Prussian Blue,” in Artists’ Pigments: A Handbook of Their History and Characteristics v.2 (Washington: National Gallery of Art, 1993), 191–211.

ii W. Linton, Ancient and Modern Colours (London, 1852).

iii J. Kirby, “Fading and Colour Change of Prussian Blue: Occurrences and Early Reports,” National Gallery Technical Bulletin (London) 14 (1993), 62-71.

iv J. Woodward, “Preparation Coerulei Prussiaci ex Germania missa ad Johannem Woodward,” Philosophical Transactions 33 (1724), 15-17.

v H. F. von Delius, Vom Preussischen Blau und der Blut Lange: Eine Erlauterungs Schrift zu des Herrn Geheimen Hof Raths und Prof. Delius (Erlangen, 1778), 3–64.

vi Berrie. vii Berrie. viii J. H. Townsend, “The Materials and Techniques of J.M.W. Turner: Pigments,” Studies in Conservation 38, no. 4 (1993), 231-254.

ix K. M. Keyes, “Japanese Print Conservation: An Overview,” Andon: Shedding Light on Japanese Art 9, no. I, 33 (1989), 6.

x W. Crawford, The Keepers of Light (Dobbs Ferry, N.Y., 1979), 67-68.

xi Berrie.