The Welsbach mantle is a device used in gas lamps to produce light. It is made from a fabric that is coated with a mixture of rare earth elements, primarily thorium and lanthanum. When heated by a flame, the mantle glows brightly, providing a more intense light than the flame alone. Invented by Carl Auer von Welsbach in the late 19th century, the mantle revolutionized outdoor and indoor lighting. It allowed gas lamps to be more efficient and brighter, making them popular for use in homes and streets before the widespread adoption of electric lighting.