use more than one dye so that diff cells, chemicals, or structures can be distinguished.
-gram stain differentiates purple staining gram positive cells from pink gram negative cells.
1-flood smear w the primary stain, crystal violet, and rinse.
2-flood smear with the mordant, iodine, and rinse
3-flood smear with decolorizing agent, a solution of ethanol and acetone, and rinse
4-flood smear with counterstain, safranin, and rinse.
-Acid fast stain is used to differentiate cells with waxy cell walls such as myobacterium and nocardia.
-Schaeffer-Fulton endospore stain=endospores cant be stained by normal techniques bc their walls are impermeable to all chemicals. This stain uses heat to drive the primary stain, malachite green into the endospore.