Hematoxylin is an oxidized product of hematoxylin, which is also used as an active ingredient for staining of cell nuclei, and can only bind to the nucleus by means of a mordant to develop color.
Hematoxylin is a frequently used stain in diagnostic pathology and research, along with eosin. Unlike iodine solution, which is a permanent stain, hematoxylin and eosin are collectively referred to as HE stains, and are one of the stains commonly used in paraffin sectioning techniques, which are widely used in histology.
Both are based on the principle of the mordant-dye-tissue complex, and in HE-stained tissue sections, the cytoplasm of the cells is red and the nuclei of the cells are blue, with the two forming a stark contrast that is easy to observe.