Histological problem- staining?

Question

In haematoxylin and eosin staining, why the biological specimen must be stained by haematoxylin dye first and then follow by eosin dye?

Why we can not stain the specimen with eosin dye first? What problem will be created if we did the eosin staining first?

Answer 1

http://www.ihcworld.com/_protocols/speci...  gives the full haematoxylin and eosin staining protocol in great detail.

It is rather complicated to explain briefly but the staining is done with haemotoxylin first due to the nature of the binding of the dye  - eosin binds electrostatically and is done second.

In acidic conditions, haematin binds to lysine residues of nuclear histones by linkage via a metallic ion mordant, in this case aluminium. (see link)