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any of the solid substances possessing various degrees of transparency and color (from colorless to dark brown) contained in resiniferous plants. Natural resins are obtained from fluids (soft resins) that are secreted from the surface of plants either spontaneously or as a result of piercing (tapping). Some natural resins, which are called fossil or semi-fossil resins, are obtained from deposits in the ground.
Natural resins melt upon heating and are insoluble in water. They dissolve or swell in organic solvents and are capable of forming films. The major components of natural resins are resin acids, monohydroxy and polyhydroxy alcohols (resinols), esters of resin acids and resin alcohols or monohydroxy phenols (tannols), and chemically inert compounds, which are apparently heterocyclic compounds. Essential oils and water may also be present; the exact chemical composition of most natural resins has not been established.
Natural resins with the greatest commercial importance include rosin, copal, shellac, amber, mastic, sandarac, dammar, and acaroid resin. Until the 1930’s, natural resins were widely used in the production of oil varnishes (copal, amber), spirit varnishes (shellac, “soft” copals, sandarac), and resin varnishes (dammar, mastic), as well as in the production of adhesives, phonograph records, linoleum, embalming agents, sealing wax, and compositions for fumigating candles. The sharp drop in demand for natural resins in recent years has been caused by the introduction of synthetic products. In the modern paint and varnish industry, rosin and the products of its modification, shellac, and amber (wastes from the production of ornaments) are the most frequently used natural resins. Natural resins are also used in the production of soaps, luminophors, polishes, sizes, cosmetic preparations, plasters, and chewing gum.
M. M. GOL’DBERG