Plants evolved many complex chemicals as defences against herbivores. That may be the origin of these resins, which are certainly not good to eat. Plants secrete resins for their protective benefits in response to injury.
The resin protects the plant from insects and pathogens. Resins confound a wide range of herbivores, insects, and pathogens. The volatile phenolic compounds may attract benefactors, that is, parasitoids or predators of the herbivores which attack the plant.
Humans value resins for their chemical constituents and uses. They are used in varnishes, adhesives, as raw materials for organic synthesis, or for incense and perfume. Fossilized resins are the source of amber. The term is also used for synthetic substances with similar properties.
Rosin, (also called 'colophony' or 'Greek pitch') is a solid form of resin. It is got from pines and some other plants, mostly conifers. Heating fresh liquid resin vaporizes light volatiles like terpenes.
Rosin is semi-transparent and yellow to black in colour. The term "colophony" comes from colophonia resina or "resin from the pine trees of Colophon", an ancient Ionic city.
Rosin has hundreds of uses, of which only a few can be mentioned here. These uses fall into groups, such as:
- Resisting slippages (increasing friction): used on stringed instruments, dancers' shoes, in gymnastics, in rock climbing, and on hands of various types of games players.
- In manufacturing soap, inks, some paints, paper, varnish, glue, soldering fluxes, and sealing wax.
- Pharmaceutical products: tablet film and enteric coating, microcapsules and nanoparticles.
- Copal and amber are natural rosins: the lighter components of tree resin evaporated and left a hardened rosin.
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Resin Facts for Kids. Kiddle Encyclopedia.