A mordant is a chemical that serves as a link between the dye and the substrate, allowing hematein to attach to the nuclear components within a cell. The result is an insoluble compound that helps adhere the dye to the cells.
The most valuable mordants for hematoxylin are salts of aluminum, iron, tungsten, and occasionally lead. These are classified respectively as :
- Alum hematoxylins
- Iron hematoxylins
- Tungsten hematoxylins
- Lead hematoxylins
The type of mordant used influences the kind of tissue components stained and the final color.
Most mordants are combined into the staining solution, although some hematoxylin stains require a pre-treatment with the mordant.