Pure erbium metal is soft, malleable and has a bright, silvery, metallic lustre. The metal is fairly stable in air and does not oxidize as rapidly as some of the other rare earth metals. Erbium lowers hardness and improves workability when added to vanadium as an alloy. An erbium-nickel alloy has an unusually high specific heat capacity at liquid-helium temperatures and is used in cryocoolers. It is also commonly used as a photographic filter. Erbium is used in a wide variety of dermatology and dental applications. It is commonly used in yttrium aluminum garnet laser crystals for cosmetic procedures and mild to medium depth skin resurfacing.