PO 5 – hansa orange R

Poor lightfastness

Manufacturer/ product code:  Kremer / 55200
Chemical Description:  dinitroaniline
Color: orange
Color Index: PO 5
Date:  1907

PO 5 – Hansa Orange R is a synthetic organic pigment belonging to the monoazo family, developed in the early 20th century as part of the broader Hansa pigment series. These pigments were designed to provide bright, economical, and versatile alternatives to traditional inorganic yellows and oranges. PO 5 occupies a vivid red-orange region of the spectrum, often described as a clean, fiery orange with a slight reddish bias.

Chemically, Hansa Orange R is based on an azo structure, where the –N=N– azo linkage is responsible for its strong visible-light absorption and high color strength. Compared to earth oranges or cadmium-based pigments, PO 5 offers significantly higher chroma and a lighter, more transparent appearance. Its transparency allows it to perform well in thin paint films, inks, and glazes, producing luminous color effects that are difficult to achieve with opaque inorganic pigments.

Historically, PO 5 found wide application in printing inks, plastics, industrial coatings, and artists’ paints, especially during the mid-20th century. In fine art, it has been appreciated for its bright mixing behavior: when combined with yellows, it produces intense warm oranges, while mixtures with reds push toward scarlet tones. With blues or greens, PO 5 quickly neutralizes into soft browns and muted violets, making it useful for controlled color modulation.

However, like many early monoazo pigments, Hansa Orange R shows moderate lightfastness rather than exceptional durability. Under prolonged exposure to strong light, especially in thin films or outdoor conditions, some fading or hue shift may occur. For this reason, it has been gradually replaced in high-end artistic and conservation contexts by more lightfast alternatives such as benzimidazolone or quinacridone oranges.

From an analytical and conservation standpoint, PO 5 is identifiable through its characteristic spectral features in Raman spectroscopy. Hansa Orange R thus represents an important step in the evolution of modern organic pigments, balancing brilliance and economy with durability limitations typical of its generation.