Pitch is a viscoelastic polymer which can be natural or manufactured, derived from petroleum, coal tar, or plants. Pitch produced from petroleum may be called bitumen or asphalt, while plant-derived pitch, a resin, is known as rosin in its solid form. Tar is sometimes used interchangeably with pitch, but generally refers to a more liquid substance derived from coal production, including coal tar, or from plants, as in pine tar.
Natural bitumen pitch, from the tar pit above the McKittrick Oil Field, Kern County, California
Bucket of pitch for use on ships
The pitch shown in this University of Queensland pitch drop experiment has a viscosity approximately 230 billion times that of water.
Bitumen is an immensely viscous constituent of petroleum. Depending on its exact composition it can be a sticky, black liquid or an apparently solid mass that behaves as a liquid over very large time scales. In American English, the material is commonly referred to as asphalt. Whether found in natural deposits or refined from petroleum, the substance is classed as a pitch. Prior to the 20th century the term asphaltum was in general use. The word derives from the ancient Greek ἄσφαλτος ásphaltos, which referred to natural bitumen or pitch. The largest natural deposit of bitumen in the world is the Pitch Lake of southwest Trinidad, which is estimated to contain 10 million tons.
Natural bitumen from the Dead Sea
Refined bitumen
The University of Queensland pitch drop experiment, demonstrating the viscosity of bitumen
Bituminous outcrop of the Puy de la Poix, Clermont-Ferrand, France