PR 172 – erythrosin B

Manufacturer/ product code:  GTI labs / CAS 15905-32-5
Chemical Description:  erythrosine
Color: red
Color Index: PR 172
Date:  1876

PR 172 – Erythrosin B is a synthetic organic pigment derived from xanthene dyes, closely related to eosin-type colorants. Chemically known as tetraiodofluorescein, erythrosin B was originally developed in the late 19th century as a dye and later adapted into pigmentary form for specific industrial and artistic uses. Its structure, rich in iodine atoms, gives rise to its distinctive and intense color properties.

Visually, PR 172 displays a bright, bluish-red to pinkish magenta hue with very high chroma. It is strongly transparent and exhibits an almost glowing quality, especially in thin films or washes. Compared to azo or quinacridone reds, erythrosin B appears cooler and more vivid, making it particularly striking in applications requiring sharp, eye-catching reds or pinks. Because of its transparency, it is best suited for glazes, inks, and optical mixtures rather than opaque passages.

From a technical standpoint, PR 172 has excellent tinctorial strength but limited lightfastness, especially in fine art contexts. Prolonged exposure to light can lead to fading, which restricts its use in permanent artworks. As a result, it is more commonly encountered in printing inks, graphic arts, security printing, and specialty applications rather than traditional artists’ paints. PR 172 thus represents a pigment where extraordinary brilliance and transparency are balanced against reduced long-term stability, highlighting the trade-offs within organic color chemistry.