Soot is primarily composed of unburned carbon particles but may also contain ash. It has a soft texture and is black or brown in color. The flammability of soot will depend on the concentration of soot and ash. Soot is combustible since it is made of carbon. Ash is noncombustible.

Creosote is a deposit that is a by-product of incomplete combustion. It is either curly, flaky deposits; gummy; or bubbly deposits. It is flammable. The next stage is glaze, which is described as a shiny, tarry substance. Glaze can form puddles or drip down and make formations that resemble black icicles. Glaze is the densest type of chimney deposit and, therefore, represents the greatest amount of fuel to burn in the event of a chimney fire. Glaze is also the most difficult type of deposit to remove from the chimney.

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