PR 90 – eosin Y

Used by Vincent Van Gogh, it’s the cause of some of the fading in his paintings

Manufacturer/ product code:  labtek
Chemical Description: bromoeosine
Color: red
Color Index: PR 90
Date:  

PR 90 – Eosin Y is a synthetic organic red dye belonging to the xanthene family, widely known for its bright pink to red-orange color and strong fluorescent properties. Chemically, it is a tetrabrominated derivative of fluorescein, with a structure that imparts both vivid coloration and notable solubility in polar solvents. While classified in the Colour Index as PR 90 in its lake or substrate-bound pigment form, Eosin Y is primarily encountered as a water-soluble dye in biological staining, inks, and commercial coloring applications.

The molecular structure of Eosin Y features a xanthene core with bromine substitutions that shift its absorption and emission toward red wavelengths, resulting in intense visual brightness and fluorescence. This makes it extremely effective in applications where visibility or optical signaling is important. However, these same structural features confer limited lightfastness and chemical stability, particularly under UV exposure, rendering PR 90 highly fugitive compared to modern quinacridone or pyrrole reds.

Historically and industrially, Eosin Y has been used in textile dyeing, food coloring (as a lake), printing inks, and histological staining. In artistic and decorative contexts, its use is mostly limited to ephemeral materials or applications requiring a strong, vibrant red-pink hue for short-term visibility rather than permanence.

From an analytical and conservation standpoint, PR 90 is significant as a dye-based, fugitive red, detectable through fluorescence microscopy, UV–Vis spectroscopy, or chromatographic methods. XRF analysis is generally ineffective due to its organic composition.