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Pitch (resin)

Pitch is the name for any of a number of highly viscous liquids which appear solid. Pitch can be made from petroleum products or plants. Petroleum-derived pitch is also called bitumen. Pitch produced from plants is also known as resin. Products made from plant resin are also known as rosin.

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Tar pitch appears solid, and can be shattered with a hard impact, but it is actually fluid. Pitch flows at room temperature, but extremely slowly. The pitch drop experiment taking place at University of Queensland is a long-term experiment which measures the flow of a piece of pitch over many years. For the experiment, pitch was put in a glass container with a hole in the bottom, and allowed to slowly drip out. Since the pitch was allowed to start dripping in 1930, only eight drops have fallen. It was calculated in the 1980s that the pitch in the experiment has a viscosity approximately 100 billion (10¹¹) times that of water^{[citation needed]}.

Pitch was traditionally used to help caulk the seams of wooden sailing vessels (see shipbuilding). It was heated, then put into a container with a very long spout. The word pitcher is said to derive from this long spouted container used to pour hot pitch.^[1] Pitch was also used to waterproof wooden containers, and is sometimes still used in the making of torches.

Production

The heating (dry distilling) of wood causes tar and pitch to drip away from the wood and leave behind charcoal. Birchbark is used to make particularly fine tar. Tar and pitch are often used interchangeably. However, pitch is considered more solid while tar is more liquid. Traditionally, pitch for waterproofing buckets, barrels and small boats was drawn from pine.^[2]