Eosin is most often used as a counterstain to hematoxylin in H&E (haematoxylin and eosin) staining. ... For staining, eosin Y is typically used in concentrations of 1 to 5 percent weight by volume, dissolved in water or ethanol. For prevention of mold growth in aqueous solutions, thymol is sometimes added.
Chemical formula: C20H6Br4Na2O5