Most incandescent lamps were designed for general use in homes and businesses. However, some required special features for use in particular locations. Westinghouse engineers designed this so-called mill lamp for use in factories and other areas subject to high levels of vibration. An intricate internal support structure absorbed vibrations and kept the filament intact for the life of the lamp. Lamps of this type were later sold as rough-service lamps. The filament itself is made from the element tantalum. Invented in 1902, tantalum filament lamps sold in the U.S. until about 1910 when tungsten lamps were introduced.