The second component of hematoxylin and eosin staining (H&E) is the counterstain, eosin. There are a variety of dyes called eosin, but the most commonly used to stain the hemalum is eosin Y. This dye is soluble in both water and ethanol. Eosin Y is a pink, acidic dye that also exhibits yellow-green fluorescence. This is visible in white light, although it is stronger with ultraviolet light, and has caused some difficulties in recording color film in years past. A related dye sometimes used is ethyl eosin. It is soluble in alcohol. Another option is eosin B, which is soluble in water and ethanol but has a bluish appearance. Although it is useful for Romanowsky stains, it is not a popular choice for sections.

By using Beslab™ Eosin Y (Water Based) solution, perfect nuclear staining can be achieved within 1-3 minutes in histopathological and cytological staining methods.