Orpiment

Orpiment, sometimes called yellow arsenic blende, is a vivid orange-yellow mineral composed of arsenic sulfide (As₂S₃). It occurs in volcanic fumaroles, low-temperature hydrothermal veins, and hot springs, and can also form through sublimation. Its name comes from the Latin *auripigmentum*—a blend of *aurum* (gold) and *pigmentum* (pigment)—referring to its rich yellow hue. Once common in art, medicine, and other uses, its application has dropped off due to its toxicity and lack of stability.

The Latin term *auripigmentum* was recorded by Pliny in the first century CE, reflecting both the mineral’s golden color and the old belief it contained gold. The Greek name *arsenikon* came from *arsenikos* (meaning “male”), based on the idea that metals had genders; this term was used by Theophrastus in the fourth century BCE. In Chinese, orpiment is called *Ci-Huang* (“female yellow”), while the Persian name *zarnikh* derives from *zar*, the Persian word for gold.

Physically, orpiment is a common monoclinic arsenic sulfide mineral. It has a Mohs hardness of 1.5 to 2 and a specific gravity of 3.49. It melts between 300 °C and 325 °C. Optically, it is biaxial negative, with refractive indices of a = 2.4, b = 2.81, and g = 3.02.

Visually, orpiment ranges from lemon-yellow to golden or brownish-yellow. It typically forms foliated, columnar, or fibrous aggregates, but can also appear botryoidal, reniform, granular, or powdery; prismatic crystals are rare. As a pigment, it is often described as lemon- or canary-yellow, sometimes golden- or brownish-yellow. In the Munsell color system, it is designated “brilliant yellow” with notation 4.4Y 8.7 /8.9.

Orpiment and realgar are closely linked minerals, often grouped together. Both are arsenic sulfides in the monoclinic crystal system, found in the same deposits and geologic settings. They share similar physical traits and human-use histories. In Chinese, orpiment is *Ci-Huang* (“female yellow”) and realgar is *Xiong-Huang* (“male yellow”), symbolizing their natural pairing in occurrence, properties, and cultural traditions. They differ in color: orpiment is a vibrant golden-yellow, while realgar is orange or reddish.

Yellow orpiment (As₂S₃) breaks down into arsenic oxides, which are water-soluble and easily migrate into surrounding materials. In painted works, these degraded oxides often spread through multiple paint layers, posing conservation challenges. Orpiment is also sensitive to light, decaying over time into a friable white arsenic trioxide. On ancient Nepalese manuscript paper, orpiment applied to deter insects has frequently turned white. To prevent degradation, conservation should limit strong light exposure, control humidity, and avoid water-based cleaning agents.

Orpiment was one of the few clear, bright-yellow pigments available to artists until the 1800s. It has been used across the Eastern Hemisphere for centuries. In Egypt, lumps of orpiment pigment were found in a tomb from the 1300s BCE. In China, it was used to color lacquer, though no written records mention this. It appears on Central Asian wall paintings from the 6th to 13th centuries. A traditional Thai painting technique still uses orpiment to make yellow ink for black paper manuscripts. Medieval European artists imported it from Asia Minor. It has been identified on Norwegian wooden altar frontals, polychrome sculptures, and folk art, including a crucifix. It was also used in Eastern Orthodox icons from Bulgaria, Russia, and the former Yugoslavia between the 12th and 16th centuries. In 1600, records show orpiment was purchased in Venice for a Romanian prince. European use was rare until the 19th century, when it appeared in Impressionist paintings.

In the medieval Norwegian church of Tingelstad, orpiment was used on the altar frontal. It was often mixed with indigo to create a dark, rich green—for example, in the Wilton Diptych (c. 1395–99), where this green appears in egg tempera on the left panel for Edmund the Martyr’s cloak. Renaissance artists like Raphael used orpiment as a yellow pigment in the *Sistine Madonna* (1513–14) for clothing and background. Tintoretto’s *Portrait of Vincenzo Morosini* (c. 1575–80) employs orpiment to replicate gold embroidery on the subject’s stole and to highlight the fur of a spotted ferret on his chest.

Despite being one of the few bright yellow pigments until the 19th century, orpiment had major drawbacks: extreme toxicity and incompatibility with common pigments like those containing lead and copper.