Soot, also called lampblack or carbon black, is a dark powdery deposit of unburned fuel residues, usually composed mainly of amorphous carbon, that accumulates in chimneys, automobile mufflers and other surfaces exposed to smoke—especially from the combustion of carbon-rich organic fuels in the lack of sufficient oxygen.

Lampblack has been used as the black pigment in paints and inks since prehistoric times, and is still widely used in printing inks, toners for xerography and laser printers, and in chemical industry. The black color of rubber tires is due to the use of lampblack as an ingredient in their vulcanisation; this use accounts for around 85% of the carbon black market.

Lampblack is easily produced experimentally by passing some noncombustible surface, such as a tin can lid or glass, closely through a candle flame. Lampblack produced in this way is among the darkest and least reflective substances known.

Lampblack is also used to coat aluminum foil that has been previously attached to a recording drum for use in a recording barograph or other instrument. The surface is scratched clear by a pointed sylus. In this case, the sooty smoke is produced by burning a small amount of camphor. After recording the image is fixed by spraying the surface with a clear lacquer. Similar coatings were used in direct recording pendulum seismometers. While not a sensitive instrument these were capable of directly recording the direction of significant horizontal shocks upon a smoked glass plate.

Cigarette smoke contains soot, which clogs up the lungs, and damages them. This causes the lung tissue to be scarred, reducing its elasticity and thus its surface area. Therefore air gets trapped in the lung, as gaseous exchange is not as efficient. This condition is called emphysema, and can eventually cause death.

Soot is in the general category of airborne particulate matter, and as such is considered hazardous to the lungs and general health when the particles are less than 5 micrometres in diameter, as such particles are not filtered out by the upper respiratory tract. Smoke from diesel engines, while composed mostly of carbon soot, is considered especially dangerous owing to both its particulate size and the many other chemical compounds present.

See also

• Indian ink
• activated carbon
• fullerenes