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Resin


Resin nonvolatile, solid or semisolid organic substances, obtained directly from certain plants as exudations, used in medicine and in the making of varnishes and plastics. Resins exude out of bark from the secretory tissues, more or less fluidly owing to the presence of volatile oil, then solidify on exposed air partly through its oxidation. They are mostly yellowish solids insoluble in water but soluble in alcohol, turpentine and spirit. Turpentine is another oleoresin obtained from the pines. Shellac is prepared from stick-lac, a resinous substance secreted on the twigs of many trees by an insect. Bangladesh has resinous plants of Damar type. Telsur and sal damar are obtained from Hopea odotata and Shorea robusta respectively.

The resin thus collected are used for varnishes and incense. Garjan balsam or Copiba is obtained from different species of Garjan tree (Dipterocarpus alatus, D. indicus, and D. turbinatus). The tree trunk yields thick, opaque oleoresin used as varnishes and lithographic ink. It is also used for smearing on woodwork. Until the beginning of 20th century this oleoresin was extracted commercially in the southern-eastern part of Bangladesh. Shellac is commercially produced in the northern districts. This resinous substance is the product of lac insect; insects derive its food from the sap of the trees and secrete resin as a sort of cocoon. Several good host plants have been selected for the cultivation of lac insect, Tachardia lacca. The common host plants are Palash (Butea monosperma), Babla (Acacia nilotica), Arhar (Cajanus cajan), Boroi (Zizyphus mauritiana). The shellac is a good insulator used mostly in the electrical industries and also as quality varnishes. [Mostafa Kamal Pasha]

See also lac dye; lac insect.