PB 24 – erioglaucine

It is one of the oldest FDA-approved color additives for food. In art supplies it is found in felt-tip pencils

Manufacturer/ product code:  GTI laboratories supplies / erythrosine B
Chemical Description:  triarylmethane dye, C37H34N2Na2O9S3, CAS 3844-45-9, C.I. 42090. food coloring E133, brilliant blue FCF
Color: blue
Color Index: PB 24
More info:  wikipedia

PB 24, known as Erioglaucine or Pigment Blue 24, is a synthetic organic pigment derived from the triarylmethane dye erioglaucine (Acid Blue 9) that has been converted into an insoluble lake form. Unlike the water-soluble dye, PB 24 is produced by precipitating erioglaucine onto an inert substrate, typically aluminum or barium salts, allowing its use as a pigment in paints and printing inks. It is characterized by a very bright, greenish-blue hue and high tinting strength, which made it attractive for graphic arts and industrial applications.

PB 24 was introduced in the late 19th to early 20th century, reflecting the transition from traditional mineral blues to synthetic organic colorants. In artworks, it is most commonly found in modern paintings, posters, colored papers, and commercial prints, rather than in classical easel painting. Its transparency and intense chroma made it suitable for glazing effects and for producing vivid mixtures, especially in combination with yellow pigments.

From a conservation perspective, PB 24 presents significant challenges. Despite its conversion into a pigment, it retains the inherent light sensitivity of triarylmethane colorants. Prolonged exposure to light can lead to fading and loss of saturation, often resulting in a dull or grayish blue. Chemically, it is invisible to elemental techniques such as XRF, requiring molecular methods for identification, including Raman spectroscopy, UV–Vis spectroscopy, or chromatographic analysis. The presence of PB 24 in an artwork is therefore an important indicator of modern materials and has implications for both dating and preventive conservation strategies.

“Handheld surface-enhanced Raman scattering identification of dye chemical
composition in felt-tip pen drawings” J Raman Spectrosc. 2018;1–10.