PBr 23 – disazo brown

Manufacturer/ product code:  Kremer / 23493
Chemical Description:  disazo condensation
Color: red
Color Index: PBr 23
Date:  —

PBr 23, commonly known as disazo brown, is a synthetic organic pigment belonging to the disazo class, characterized by the presence of two azo (–N=N–) linkages connecting aromatic rings. Introduced in the early 20th century, it was developed as part of the expanding range of industrial organic pigments designed to provide strong, economical alternatives to traditional earth and natural brown pigments. Disazo brown typically presents a warm, reddish- to yellowish-brown hue with high tinting strength and good covering power.

Chemically, PBr 23 is produced by coupling diazotized aromatic amines with suitable coupling components, followed by precipitation to obtain an insoluble pigment. It shows good dispersibility in a variety of binding media, including oil, acrylic, alkyd, and printing ink vehicles. Its chromatic strength makes it particularly useful for darkening mixtures, producing rich shadows, and formulating complex browns and neutral tones in modern palettes.

From a conservation perspective, PBr 23 generally exhibits moderate to good lightfastness, superior to many early organic dyes, though prolonged exposure to intense light can still result in gradual fading or slight hue shifts. It is chemically stable under neutral conditions but may be sensitive to strong acids or alkalis. As an organic pigment, it cannot be detected by elemental techniques such as XRF. Identification therefore relies on molecular analytical methods, including Raman spectroscopy, FTIR, and chromatographic techniques. The presence of disazo brown in an artwork is indicative of 20th-century materials and is particularly relevant for the study of modern paintings, design objects, and commercial prints.