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Chimney deposits can be found in a variety of forms but can be divided into three basic types as shown below:
Soot - Soot is primarily composed of unburned carbon particles but may also contain ash. Soot has a soft texture and will be black or brown in color. The flammability of soot will depend on the concentration of soot and ash. Soot, since it is made of carbon, is combustible. Ash is noncombustible.
Creosote - Creosote can be defined as a combustible deposit in the venting system which begins as condensed wood smoke including tar fogs and vapors. Creosote is a by-product of incomplete combustion. If a fuel is fully burned there will be no smoke and, therefore, no creosote. Creosote will be hard brown or black and form either curly, flaky deposits or bubbly deposits in the venting system. Creosote is flammable.
Glaze - Glaze is a form of deposit that presents itself as a shiny, tarry substance. Glaze can form puddles or drop 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. | 
