Haematoxylin or hematoxylin (/ˌhiːməˈtɒksɪlɪn/), also called natural black 1 or C.I. 75290, is a compound extracted from heartwood of the logwood tree (Haematoxylum campechianum) with a chemical formula of C16H14O6. This naturally derived dye has been used as a histologic stain, ink and as a dye in the textile and leather industry. As a dye, haematoxylin has been called Palo de Campeche, logwood extract, bluewood and blackwood. In histology, haematoxylin staining is commonly followed (counterstained), with eosin, when paired, this staining procedure is known as H&E staining, and is one of the most commonly used combinations in histology. In addition to its use in the H&E stain, haematoxylin is also a component of the Papanicolaou stain (or PAP stain) which is widely used in the study of cy