Shellac
Lac (Laccifer Lacca) are scale insects (insects that attach themselves in great numbers to plants and trees) which drain the sap from the bark of their host tree, allowing them to secrete lac resin which is scraped off and manufactured into shellac. Around 300,000 insects are used to produce 1kg of lac resin [1,2].
The Life of a Lac
Lac are grown on managed trees which are pruned in order to stimulate the growth of young shoots. These young shoots provide sap which the lac insect can use as food. Four to six months after the trees have been pruned, a number of lac-infested branches are tied to them. These branches contain mature female lacs (broodlac) who lay up to 100 eggs which hatch out into larvae.
These small red larvae crawl out of the broodlac and settle on the twigs [3]. They insert their long suctorial mouthpart or proboscis into the bark and draw out food (tree sap). The sap is transformed to lac resin in the body and then secreted around the insect where it forms a hard protective covering to prevent attack by predators. Eventually the lac resin from each insect joins together, covering the entire swarm.
The insects mature into adults under this protective layer, becoming sexually mature after about eight weeks. The males fertilise the females and then die. After fourteen weeks the females lay their eggs and also die.
As the new generation of lacs begin to emerge, the resin encrusted branches are harvested and the resin is separated out. At this stage the resin is called 'sticklac'. It is further processed to 'seedlac' and finally to 'shellac'. A number of branches are retained to tie to more trees and so produce the next crop [4].
Usually the young lacs are given the opportunity to escape to a new home before the branches are harvested but some will inevitably remain and therefore be scooped up and killed during harvesting.
Manufacturing Process
The sticklac is crushed into small grains, sieved, washed and dried, removing impurities. This semi-refined product, called seedlac, is further refined by a system of hot melting, filtration and stretching into thin sheets which are subsequently broken into brittle flakes called shellac [5].
Areas of Cultivation
India and China are the main areas in the world where lac is cultivated. Since the late 1940s, international trade in seedlac and shellac has declined due to competition from synthetic alternatives.
Uses of Shellac
Shellac has been utilised in the manufacture of many products over the years. Today uses of shellac include as a component of paint and varnish, a glaze for fruit, a coating for tablets, hair lacquer, nail varnish and confectionery [5].
Shellac can not be used to glaze organic fruit under organic standards.
Lac By-Products and Derivatives
Shellac acid derivatives include aleuritic acid, jalaric acid and shellolic acid. By-products obtained during manufacture of shellac include lac dye, molamma, kiri, passewa, and shellac wax.
Lac dye (laccaic acid) is obtained during the washing of seedlac. Shellac wax is retrieved from shellac resin, and has properties similar to carnauba wax.
Alternatives
Carnauba wax, which comes from the leaf of a type of palm tree, makes an excellent non-toxic glaze for foodstuffs, and can also be used in polishes and varnishes.
References
- http://www.tolaramshellac.com/product.html (accessed 30 Nov 2007)
- http://www.antcons.com.au/Shellac.html (accessed 30 Nov 2006)
- (1913) The Story of Shellac, USA: Wm. Zinsser & Co. Inc.
- http://www.artisansofthevalley.com/ed_shellac.shtml (accessed 30 Nov 2007)
- Sarkar, P. C. (2001) Basic Information on Lac / Shellac, India: Indian Lac Research Institute.
- http://www.tolaramshellac.com/uses.html