Orpiment

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.