Pararealgar is a yellow crystalline form of arsenic sulfide (As₄S₄), distinct from realgar, its orange-red counterpart. It forms through the photochemical degradation of realgar. Orpiment (As₂S₃), on the other hand, is a separate compound with a golden-yellow hue. These differences are crucial for identifying pigments in historical artworks.
Pararealgar in Art: Rediscovering Rembrandt’s Rare Pigment
Rembrandt's The Night Watch continues to captivate, not only for its artistic brilliance but also for the groundbreaking discoveries about its materials. Recent research has unearthed fascinating details about Rembrandt's palette, particularly the use of a rare pigment called pararealgar and its semi-amorphous form. These findings offer artists valuable lessons in historical techniques, pigment properties, and the importance of understanding material behavior over time.
What is Pararealgar?
Pararealgar is a yellow arsenic sulfide mineral closely related to realgar, an orange-red compound. Unlike realgar, which degrades into pararealgar upon exposure to light, the pararealgar discovered in The Night Watch shows no evidence of such transformation. This suggests that Rembrandt deliberately chose this pigment, challenging long-held assumptions that pararealgar was solely a degradation product.
This discovery is particularly important because it expands our understanding of the arsenic sulfide pigments available to 17th-century artists. The presence of both crystalline pararealgar and its semi-amorphous variant implies deliberate use for specific visual effects, offering a richer palette of yellows and oranges than previously documented.
The four images from top left (a) Rembrandt van Rijn (1606–1669), The Night Watch, 1642, oil on canvas, dimensions: 379.5 cm x 453.5 cm, housed at the Rijksmuseum, inventory number SK-C-5. (b) A close-up of Willem van Ruytenburch’s buff coat and sleeves, showing where samples SK-C-5_016 and SK-C-5_017 were taken. (c) An X-ray fluorescence (MA-XRF) map highlighting arsenic (As-K) levels in the buff coat, as marked by the white rectangle in panel (b). (d) A stereomicroscope image of the area marked in red in panel (c), showing a bright orange paint spot identified as an arsenic-rich area (red arrow). (From De Keyser, 2024)
Rembrandt's Choices: A Palette of Innovation
Rembrandt's use of arsenic sulfide pigments in The Night Watch demonstrates his mastery of material selection for expressive purposes. Found in the embroidered coat of Willem van Ruytenburch, the pigments were used alongside traditional materials like lead-tin yellow and vermilion to create vibrant orange hues.
The presence of pararealgar and its semi-amorphous variant indicates intentional layering. These pigments provided Rembrandt with the tools to achieve dynamic highlights and subtle tonal shifts. The sharp-edged, glass-like particles of pararealgar also contrast texturally with other pigments, enhancing the painting's overall vibrancy.
Properties of Pararealgar: What Artists Should Know
Artists using or recreating arsenic-based pigments should note these critical properties:
Color Range and Stability: Pararealgar exhibits a rich yellow tone, while its semi-amorphous form adds redder hues. Unlike other arsenic pigments, its use here shows remarkable stability, indicating it can retain its intended color under specific conditions.
Toxicity: As an arsenic compound, pararealgar poses significant health risks. Artists must handle it carefully, using protective gear and ensuring proper studio ventilation.
Light Sensitivity: While realgar degrades into pararealgar upon light exposure, pararealgar itself appears more resistant, making it a unique addition to a painting's tonal repertoire.
The Making of Pararealgar Pigments
Historical sources suggest that pararealgar pigments were likely manufactured using dry processes such as roasting and sublimation. These methods involved heating natural arsenic compounds like realgar and orpiment, often adding sulfur to refine the final product.
In 17th-century Amsterdam, arsenic pigments were imported from production centers in Germany and Italy. Artists likely purchased these materials from specialized pigment dealers, underscoring the interconnectedness of art, trade, and early chemical innovation.
Lessons for Modern Artists
The rediscovery of pararealgar in The Night Watch offers practical insights for today's artists:
Material Knowledge: Understanding pigment properties can inform better material choices, especially for restorers and those replicating historical techniques.
Experimentation: Rembrandt's innovative use of rare pigments invites modern artists to experiment with unconventional materials to expand their creative expression.
Conservation Awareness: Artists should consider the long-term stability of materials, particularly when choosing light-sensitive pigments.
The revelation of pararealgar in Rembrandt's The Night Watch exemplifies how scientific inquiry can enrich artistic practice. By unraveling the mysteries of historical pigments, we not only honor the ingenuity of past masters but also inspire contemporary artists to approach their materials with curiosity and care.
Bibliography
De Keyser, Nouchka, et al. "Discovery of Pararealgar and Semi-Amorphous Pararealgar in Rembrandt’s The Night Watch: Analytical Study and Historical Contextualization." Heritage Science 12, no. 237 (2024). DOI:10.1186/s40494-024-01350-x.
Vermeulen, Marc, et al. "Identification by Raman Spectroscopy of Pararealgar as a Starting Material in the Synthesis of Amorphous Arsenic Sulfide Pigments." Dyes and Pigments 149 (2018): 290-297. DOI:10.1016/j.dyepig.2017.10.009.
Pigments Mentioned in this Article
Frequently Asked Questions
What is pararealgar, and how is it different from realgar and orpiment?
How does realgar degrade into pararealgar?
Realgar degrades into pararealgar when exposed to light, particularly ultraviolet rays. This photochemical reaction rearranges the molecular structure of realgar, producing pararealgar as a yellow crystalline product. Over time, further degradation can lead to the formation of arsenic trioxide.
Did Rembrandt and other Old Masters deliberately use pararealgar?
Evidence suggests Rembrandt intentionally used pararealgar in The Night Watch, as indicated by its presence in undisturbed paint layers. This challenges the assumption that pararealgar in artworks is always a degradation product of realgar.
Can artists today safely use realgar or pararealgar in paintings?
Artists can use realgar or pararealgar, but they must take precautions due to their toxicity. Protective gear, proper ventilation, and UV-blocking varnishes are essential for safe handling and to prevent degradation.
How were arsenic-based pigments like pararealgar and realgar manufactured historically?
These pigments were often produced using dry processes such as roasting or sublimating natural arsenic compounds like orpiment and realgar. Historical recipes also involved adding sulfur to refine the pigments’ quality.
How can conservators detect pararealgar in historical paintings?
Conservators use advanced techniques, such as Raman spectroscopy and synchrotron-based X-ray diffraction, to identify pararealgar. These methods differentiate it from other arsenic compounds by analyzing unique vibrational and structural signatures.
Why was pararealgar mistaken for orpiment historically?
Pararealgar was historically mistaken for orpiment due to their similar yellow coloration. Before modern analytical tools like Raman spectroscopy, visual identification was often unreliable, leading to misclassification.
What are the challenges in preserving paintings with pararealgar or realgar?
The main challenges include their light sensitivity and tendency to degrade over time. Conservators must limit light exposure and maintain controlled environmental conditions to stabilize these pigments.
George O’Hanlon is the technical director of Natural Pigments, and executive director of Iconofile, a nonprofit educational organization dedicated to promoting understanding of sacred art. George received his fine arts education and apprenticeship in Mexico. Upon return to the United States, he worked as creative director for advertising agencies in Silicon Valley, working on such major accounts as Sony, Hewlett-Packard, and Ricoh. He founded an agency later acquired by the chemical giant, Shin-Etsu. There he served as vice-president of U.S. marketing. In 1992, he studied traditional art techniques abroad. Then in 2001, co-founded Iconofile and in 2003 Natural Pigments to promote an understanding of these practices. Since that time he has formulated hundreds of artists’ paints and materials, including Ceracolors, a waterborne wax paint...
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