In staining, a mordant is a chemical that helps adhere the dye to the cells or tissue by serving as a link between the dye and the substrate. The result is an insoluble compound that intensifies or fixes the dye or stain. In microbiology, a mordant is a compound used to hold down molecules of a stain onto a microorganism. The term "mordant" comes from the Latin word "mordere," which means "to bite". The most useful mordants for hematoxylin, a commonly used stain in diagnostic histology of animal tissues, are salts of aluminum, iron, tungsten, and occasionally lead. The type of mordant used influences the type of tissue components stained and the final color. There are three methods used for mordanting: pre-mordanting, meta-mordanting, and post-mordanting. The processes involving trapping agents stain perfectly well if the step is omitted, while processes requiring a mordant dont stain unless the mordant is used.