PO 73 – pyrrole orange

Poor lightfastness

Manufacturer/ product code:  Kremer / 23178
Chemical Description:  diketo-pyrrolo-pyrrole
Color: orange
Color Index: PO 73
Date:  from 1984

PO 73 – Pyrrole Orange is a modern synthetic organic pigment belonging to the pyrrole-based pigments, a family developed in the late 20th century to combine high chroma, excellent lightfastness, and strong chemical stability. PO 73 occupies the orange region between red-leaning oranges and warm reds, offering a clean, intense hue that is both vibrant and controlled, without the muddiness often associated with traditional earth or cadmium-based oranges.

Chemically, Pyrrole Orange is related to the same class of compounds that includes pyrrole reds, known for their robust molecular structure. This stability translates into outstanding lightfastness (typically ASTM I), making PO 73 suitable for demanding applications where long-term color permanence is essential. Unlike historical orange pigments such as realgar or chrome orange, PO 73 contains no heavy metals, aligning with modern safety and environmental standards.

In artistic practice, PO 73 is valued for its high tinting strength and opacity, allowing it to assert itself strongly in mixtures while still maintaining clarity. It produces luminous oranges when used alone and creates clean, saturated blends with yellows and reds, without excessive dulling. Mixed with blues, it yields controlled neutrals rather than muddy browns, a characteristic appreciated by painters seeking chromatic balance.

From a conservation and technical perspective, Pyrrole Orange shows good resistance to solvents, acids, and alkalis, making it compatible with a wide range of binders, including oil, acrylic, and alkyd media. Its predictable behavior under aging and light exposure has led to its adoption not only in fine art materials but also in industrial coatings and plastics, where durability is critical.