A variation on the "central-draught" lamp is the mantle lamp. The mantle is a roughly pear-shaped mesh made of fabric placed over the burner. The mantle typically contains thorium or other rare-earth salts; on first use the cloth burns away, and the rare-earth salts are converted to oxides, leaving a very fragile structure, which incandesces (glows brightly) upon exposure to the heat of the burner flame. Mantle lamps are considerably brighter than flat- or round-wick lamps, produce a whiter light and generate more heat. Mantle lamps typically use fuel faster than a flat-wick lamp, but slower than a center-draught round-wick, as they depend on a small flame heating a mantle, rather than having all the light coming from the flame itself.