Pigment

Orpiment, a striking yellow pigment made from arsenic trisulfide (As₂S₃), has been used for centuries across various cultures for artistic and decorative purposes. This vivid yellow hue, also known as king’s yellow, was highly prized despite its toxic properties due to the presence of arsenic. Alongside realgar, its red arsenic sulfide counterpart, orpiment, has a rich history that spans continents and artistic traditions.[i] Its brilliant yellow color and chemical properties made it a valuable pigment, though it also presented challenges in terms of stability and safety. The pigment was also called Chinese yellow when imported from Asia in the early 19th century.[ii] Historically, both natural and artificial forms of orpiment were used. Artificial orpiment, also known as king’s yellow, became especially prevalent in Europe during the 18th century.[iii]

Historical Use

Orpiment has been a pigment for thousands of years, with early examples in ancient Egypt and Mesopotamia. In Egypt, orpiment was identified in tomb decorations from the New Kingdom period (16th-11th centuries BCE) and used in cosmetics, indicating its dual role as a decorative material and an element of personal adornment.[iv] Orpiment has also been found in Assyrian artifacts, Persian manuscripts, and Chinese lacquerware, showcasing its wide geographical distribution.[v]

Orpiment was a popular pigment in Europe from medieval times through the Renaissance. It was often used in illuminated manuscripts, panel paintings, and wall frescoes. One notable occurrence of orpiment is in the palette of the famous Renaissance artist Jan van Eyck, who used it in his vibrant works.[vi] Despite its toxicity, orpiment was valued for its brilliance and opacity, making it a preferred choice for highlights and decorative details.

Orpiment’s use persisted into the 19th century, especially in the production of watercolor paints and oils. However, as more stable and less toxic yellow pigments like cadmium yellow became available, orpiment gradually fell out of favor. [vii]

Chemical Composition and Properties

Orpiment is composed of arsenic trisulfide (As₂S₃), giving it its distinctive lemon-yellow or canary-yellow color. The pigment is known for its brilliance and high opacity, making it popular in various artistic media. It has a refractive index of around 2.4 to 3.0, giving it a strong covering power compared to other pigments. [viii]

However, orpiment has some notable weaknesses. It is incompatible with certain other pigments, such as those containing lead or copper, and can cause the darkening or degradation of nearby colors. This was well-known by medieval artists, who often avoided mixing orpiment with lead white or verdigris, as the combination would lead to discoloration. [ix]

In terms of stability, orpiment is sensitive to light and can gradually fade or alter when exposed to air and moisture. Over time, it can degrade into arsenic trioxide (As₂O₃), a more toxic compound, especially when exposed to high humidity or heat. The pigment also decomposes in water, limiting its applications in aqueous media like frescoes.[x]

References

[i] R. D. (Rosamond Drusilla) Harley 1934-, Artists’ Pigments, c. 1600-1835 : A Study in English Documentary Sources, Second revised edition. (London : Archetype, 2001).

[ii] Harley.

[iii] Robert L. Feller et al., eds., “2 Orpiment and Realgar,” in Artists’ Pigments: A Handbook of Their History and Characteristics v.2 (Washington: National Gallery of Art, 1993), 67–87.

[iv] B. Guineau, “Microanalysis of Painted Manuscripts and of Colored Archeological Materials by Raman Laser Microprobe,” Journal of Forensic Sciences 29, no. 2 (1984): 471–85, https://doi.org/10.1520/JFS11695J.

[v] Edward H. Schafer, “Orpiment and Realgar in Chinese Technology and Tradition,” Journal of the American Oriental Society 75, no. 2 (1955): 73–89, https://doi.org/10.2307/595009.

[vi] Faber Birren 1900-1988., History of Color in Painting with New Principles of Color Expression. (New York : Reinhold Pub. Corp., 1965).

[vii] Feller et al., “2 Orpiment and Realgar.”

[viii] Feller et al.

[ix] Feller et al.

[x] Feller et al.

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.