Produced by the partial combustion or thermal decomposition of hydrocarbons. Several methods are used, including the furnace black, thermal black, lamp black and acetylene black processes. The furnace black process is the most common. In this process, natural gas (or another fuel) is burned to form a hot gas stream that is directed into a tunnel. An aromatic oil is sprayed in and the black forms as the gas moves down the tunnel. The reaction is quenched with the addition of water, and the product is collected as a low density powder (fluffy black) or is further processed into millimeter sized pellets.