A gas mantle is a device that gives off considerable light when heated. The name refers to its original power source, existing gas lights which filled the streets of Europe and North America in the late 19th century, mantle referring to the way it hung above the flame. Today they are still used for portable camping lanterns and pressure lamps.

The gas mantle was one of the many inventions of Auer von Welsbach, a chemist who studied rare earth elements in the 1880s. His first process used a mixture of 60 percent magnesium oxide, 20 percent lanthanum oxide and 20 percent yttrium oxide which he called Actinophor. To produce a mantle guncotton is impregnated with the mixture and then heated; the cotton burns away leaving a solid (but fragile) mesh of ash.

These original mantles gave off a green-tinted light and were not very successful, and his first company formed to sell them failed in 1889. A new mixture of 99 percent thorium(IV) oxide and 1 percent cerium oxide gave off a much "whiter" light, and after introducing it commercially in 1892 it quickly spread throughout Europe. The gas mantle remained an important part of street lighting until the widespread introduction of electric lighting in the early 1900s.

A mantle is basically a small sock made of silk or asbestos. Asbestos can withstand high temperatures, but is also toxic. Silk-based mantles are extremely brittle once first burned, and must be replaced frequently.

Thorium is radioactive, and pure thorium becomes more radioactive as it ages owing to its decay products. It should be handled with care. Owing to concerns about the radioactivity of thorium, alternatives are now used in some countries, but these are more expensive and less efficient.

See also: mantle (disambiguation)