Iodine is the mordant in Gram's Staining method. Applied after the crystal violet to chemically bond the dye to the bacterial cell walls. Unstabilized iodine is designed to be prepared as a working solution. Concentrated iodine is added to a diluent when the product is ready to use. Must be mixed and is not ready-to-use until the concentrated is thoroughly incorporated in the diluent. FDA approved for in vitro diagnostic use.