The most common fixative is formalin (10% neutral buffered formaldehyde in water). The most common fixative is formalin, although frozen section fixing is also common. The most commonly used fixative in histology is formaldehyde. The formaldehyde vapor can also be used as a fixative for cell smears. Ambroxide is used in perfumery for creating ambergris notes and as a fixative. Historically ferrous sulfate was used in the textile industry for centuries as a dye fixative. In perfumery it is used as a fixative. Paraformaldehyde is not a fixative; it must be depolymerized to formaldehyde in solution. Pasties are usually applied with a special tape or glue fixative, often gum arabic. Acrolein is sometimes used as a fixative in preparation of biological specimens for electron microscopy. Modern embalming is not done with a single fixative. An example is mercury pigment left behind after using Zenker's fixative to fix a section. A fixative that displaced the soaps and oils used for this purpose. Due to its excellent fixative properties, vetiver is used widely in perfumes. It is used as a fixative in perfumes and has an intense fragrance.