A group of high-viscosity or solid hydrocarbons obtained from naturally occurring deposits or from the residue of petroleum refining, commonly used as additives for oil-base and water-base muds. Molten asphalt can be further processed by heating and passing air through the melt to oxidize and polymerize its components. Cooled, air-blown asphalt is glassy and can be ground. It has a high softening point and polar sites that offer emulsion-stabilizing qualities and affinity for clays and shales.