Basic Yellow 2 C.I. Number 41000 CAS Number 2465-27-2 Synonyms: Auramine O, Basic yellow 2, Pyocatanium, aureum, Aizen auramine, Pyoktanin Yellow, Canary Yellow, Pyoktanin. Auramine O is a diarylethene dye used as a fluorescent stain. In its pure form, Auramine O appears as yellow needle crystals. It is very soluble in water and soluble in ethanol. Application area: Acrylic fibers, silk, and cotton fiber also applied in the dyeing of leather, paper, hemp, and viscose, Direct printing and blotch discharge printing of tannin mordant dyed cotton & used to produce color lake and used in inks.