Tar

What tar is

Tar can be produced from carbon-rich materials such as coal, wood, petroleum, peat and other organic matter. The words tar and pitch can be used interchangeably. Tar tends to be used for more liquid substances and pitch for more solid ones. Asphalt, which is naturally occurring pitch, may also be called mineral tar or mineral pitch. Mineral products resembling tar can be produced from fossil hydrocarbons, such as petroleum. The by-products of wood tar are turpentine and charcoal.

Birch, pine and cade tars

Birch bark tar is mainly composed of triterpenoid compounds of the lupane and oleanane family. Its most characteristic molecules are betulin and lupeol, which are also present in birch bark. Birch bark tar oil has strong antiseptic properties, owing to a large amount of phenol derivatives and terpenoid derivatives. Pine tar consists primarily of aromatic hydrocarbons, tar acids, and tar bases. Its components vary according to the pyrolytic process and the origin of the wood. Juniperus oxycedrus, vernacularly called cade, is a species of juniper native across the Mediterranean region. Cade oil has, on rare occasions, caused severe allergic reactions in infants.

Coal tar

Coal tar is a viscous dark liquid that is a by-product of deriving coke and coal gas from coal. The International Agency for Research on Cancer lists coal tars as Group 1 carcinogens. The use of coal tar in cosmetic products was forbidden in the European Union by a directive in 2009.

Other uses of wood tar

Since prehistoric times, wood tar has been used as a water-repellent coating for boats, ships, sails, and roofs. Wood tar is microbicidal. Wood tar is still used as an additive in the flavoring of candy, alcohol, and other foods. Pine tar has a long history as a wood preservative, as a wood sealant for maritime use, in roofing construction and maintenance, and in soaps. Pine tar was used as a preservative on the bottoms of traditional Nordic-style skis until modern synthetic materials replaced wood in their construction. Pine tar is used in baseball to enhance the grip of a hitter's bat.

History

Birch bark tar began to be used as an adhesive in the Middle Paleolithic. Techniques for producing tar from wood were known in ancient Greece and have probably been used in Scandinavia since the Iron Age. Strong indications link cone-shaped pits north of Uppsala, Sweden, to pine tar production, and the oldest of three dated pits goes back to 540-380 BCE. The Roman naturalist Pliny the Elder describes how, in Europe, tar is produced through the destructive distillation of pine wood. In Finland, then a part of Sweden, large-scale tar production began in the early 17th century. By the late 17th century, tar was Sweden's third most valuable export commodity. Sweden exported 13,000 barrels of tar in 1615 and 227,000 barrels in the peak year of 1863. The largest user was the Royal Navy of the United Kingdom. Demand for tar declined with the advent of iron and steel ships.

Russia leather is a water-resistant leather, oiled with birch bark oil after tanning. This leather was a major export good from seventeenth- and eighteenth-century Russia. Birch bark tar oil was used in the eighteenth century alongside civet and castoreum and many other aromatic substances to scent the fine Spanish leather Peau d'Espagne. Coal tar has been produced since about 1665.

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Related: Coal Tar Pitch · Motor Oil · Petroleum