Fatwood

Fatwood, also known as "fat lighter," "lighter wood," "rich lighter," "pine knot," "lighter knot," "heart pine" or "lighter'd" [sic], is derived from the heartwood of pine trees. This resin-impregnated heartwood becomes hard and rot-resistant. The stump (and tap root) left in the ground after a tree has fallen or has been cut is an excellent source of fatwood. Other locations, such as the joints where limbs intersect the trunk, can also be harvested. Although most resinous pines can produce fatwood, in the southeastern United States the wood is commonly associated with longleaf pine (Pinus palustris), which historically was highly valued for its high pitch production.

The commercial use of fatwood from stumps stemmed from its use to make pitch and pine tar. In 1648, a company was formed in Sweden called Norrländska Tjärkompaniet (The Wood Tar Company of North Sweden), and was given exclusive export rights[for pinetar - see separate topic- not fatwood] by the King of Sweden.

Coniferous tree sap is a viscous liquid, that contains terpene, a volatile compound which is a type of hydrocarbon. Over time the evaporation of the terpene changes the state of the sap; it slowly gets thicker until it hardens into resin. New fatwood leaks the sticky sap, while in aged fatwood the sap has hardened and is no longer sticky. At every stage of the aging process, fatwood will burn readily, even when wet.

Because of the flammability of terpene, fatwood is prized for use as kindling in starting fires. It lights quickly even when wet, is very wind resistant, and burns hot enough to light larger pieces of wood. A small piece of fatwood can be used many times to create tinder by shaving small curls and using them to light other larger tinder. In Louisiana "fatwood" is known as "rich lighter" and cut slivers are what is referred to as "kindling" because of the abundance. The pitch-soaked wood produces an oily, sooty smoke, and it is recommended that one should not cook on a fire until all the fatwood has completely burned out. The smoke produced by "fatwood" is considered to be an excellent bug (especially mosquito) repellent (although this is unproven).

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Wikipedia