Resin is a hydrocarbon secretion of many plants, particularly coniferous trees. It is valued for its chemical constituents
and uses, such as varnishes and adhesives, as an important source of raw materials for organic synthesis, or for incense and
perfume. Fossilized resins are the source of amber. Resins are also a material in nail polish.
The term is also used for synthetic substances of similar properties. Resins have a very long history and are mentioned by
both ancient Greek Theophrastus and ancient Roman Pliny the Elder, especially as the forms known as frankincense and myrrh.
They were highly prized substances used for many purposes, especially perfumery and as incense in religious rites.
The resin produced by most plants is a viscous liquid, composed mainly of volatile fluid terpenes, with lesser components of
dissolved non-volatile solids which make resin
thick and sticky. The most common
terpenes in resin are the bicyclic terpenes alpha-pinene, beta-pinene, delta-3 carene and sabinene, the monocyclic terpenes
limonene and terpinolene, and smaller amounts of the tricyclic sesquiterpenes, longifolene, caryophyllene and delta-cadinene.
Some resins also contain a high proportion of resin acids. The individual components of resin can be separated by fractional
A few plants produce resins with different compositions, most notably Jeffrey Pine and Gray Pine, the volatile components of
which are largely pure n-heptane with little or no terpenes. The exceptional purity of the n-heptane distilled from Jeffrey
Pine resin, unmixed with other isomers of heptane, led to its being used as the defining zero point on the octane rating
scale of petrol quality. Because heptane is highly flammable, distillation of resins containing it is very dangerous. Some
resin distilleries in California exploded because they mistook Jeffrey Pine for the similar but terpene-producing Ponderosa
Pine. At the time the two pines were considered to be the same species of pine; they were only classified as separate species
Some resins when soft are known as 'oleo-resins', and when containing benzoic acid or cinnamic acid they are called balsams.
Other resinous products in their natural condition are a mix with gum or mucilaginous substances and known as gum resins.
Many compound resins have distinct and characteristic odors, from their admixture with essential oils.
Certain resins are obtained in a fossilized condition, amber being the most notable instance of this class; African copal and
the kauri gum of New Zealand are also procured in a semi-fossil condition.