BITUMEN
Pitch is a viscoelastic polymer which can be natural or manufactured, derived from petroleum, coal tar, or plants.
Pitch is a viscoelastic polymer which can be natural or manufactured, derived from petroleum, coal tar, or plants. Various forms of pitch may also be called tar, bitumen, or asphalt. Pitch produced from plants is also known as resin. Some products made from plant resin are also known as rosin.
Pitch was traditionally used to help caulk the seams of wooden sailing vessels (see shipbuilding), and to coat earthenware vessels for the preservation of wine. Pitch may also be used to waterproof wooden containers and in the making of torches. Petroleum-derived pitch is black in colour, hence the adjectival phrase, "pitch-black".
The viscoelastic properties of pitch make it well suited for the polishing of high-quality optical lenses and mirrors. In use, the pitch is formed into a lap or polishing surface, which is charged with iron oxide (Jewelers' rouge) or cerium oxide. The surface to be polished is pressed into the pitch, then rubbed against the surface so formed. The ability of pitch to flow, albeit slowly, keeps it in constant uniform contact with the optical surface.
Chasers pitch is a combination of pitch and other substances, used in jewellery making.
