Ytterbium, holmium, thulium, and erbium are other common "dopants" in solid-state lasers. In 1878, erbium ores were found to contain the oxides of holmium and thulium. The erbium doped amplifier is a high gain amplifier. Some commonly used lasers types in soft tissue surgery include erbium, diode, and CO. When added to vanadium as an alloy, erbium lowers hardness and improves workability. IPG then developed erbium fiber amplifiers using new a new pump design and fiber solution. The isotopes of erbium range in atomic weight from () to (). Metallic erbium in dust form presents a fire and explosion hazard. Humans consume 1 milligram of erbium a year on average. Erbium and ytterbium ions are common active species in such lasers. Erbium can also be used in erbium-doped waveguide amplifiers. Erbium lasers are both hard and soft tissue capable. Erbium is slightly toxic if ingested, but erbium compounds are not toxic. Erbium lasers are excellent cutters, but provide minimal hemostasis. Erbium does not have a biological role, but erbium salts can stimulate metabolism.