Resin secretion occurs in special cavities or in many plant species. They are formed in the specialized structures called passages ducts. Resins exude or ooze out from the bark of the trees and tend to harden on exposure to air. With the exception of lac, which is produced by the lac insect (Kerria lacca), all other natural resins are of plant origin. Natural resins of particular importance to the furniture coatings are rosin, damar, copal, sandarac, amber and manila.
The principal characteristics of resins are:
They are insoluble in water.
They are soluble in ordinary solvents like alcohol, ether and turpentine.
They are brittle, amorphous and are transparent or semi-transparent.
They have a characteristics luster, are ordinarily fusible and when ignited,resins burn with a smoky flame.
Natural gums
Gums are a group of plant products, formed primarily due to the disintegration of plant cellulose. This process is known as gummosis.Gums are produced by members of a large number of families but exploitation is restricted to of commercial a few tree species Leguminosae, Sterculiaceae and Combretaceae families. The important gum yielding trees are Acacia nilotica (babul), A catechu (khair), Steruculia urens (kullu), Anogeissus latifolia (dhawra), Butea monosperma (palas), Bauhinia retusa (semal), Lannea coromandelica (lendia) and Azadirachta indica (neem). Gums is also extracted from seeds of certain plants like guar, tamarind, Cassia tora etc. Guar gum is the prominent seed based natural gum.
Gum resins
Gum-resins are a mixture of both gums and resins and possess the properties of both the groups. They contain traces of essential oils.These are usually derived from the plant growing in dry and arid regions. Some of the commonly used gum-resins ale asafoetida, myrrh, salai, guggul etc.
