Shellac
From Freepedia
Shellac is a waxy secretion of the lac insect Coccus lacca, found in the forests of Assam and Thailand. Freed from wood it is called "seedlac." Once it was said that Shellac was a resin obtained from the wings of a beetle found in India. It was not so, shellac being otained from an excretion from the female beetle, harvested from the bark of a tree where she deposited it to provide a sticky hold on the trunk. "Authority 1" said that this hold was necessary during mating with the non-stick capable male. "Authority 2" said that it enabled her to hold to the tree while feeding. When purified, the chemical is of the form of yellow/ brown leaflets, this possibly providing the basis for the "Wing Source Story". Shellac is a natural polymer and is chemically similar to synthetic polymers, thus considered a natural plastic. It can be molded by heat and pressure methods, so it is classified as thermoplastic.
It was used from mid-19th century on to produce small goods like picture frames, boxes, toilet articles, jewellery, inkwells and even dental plates.
It is soluble in alkaline solutions such as ammonia, sodium borate, sodium carbonate, and sodium hydroxide, and also in various organic solvents.
When dissolved in acetone or alcohol, shellac yields a varnish of superior gloss and hardness and is available in numerous grades. It is used in the traditional "French polish" method of finishing furniture. Orange shellac is bleached with sodium hypochlorite solution to form white shellac. Because it is compatible with most other finishes, shellac is also used as a barrier or primer coat on wood to prevent the bleeding of resin or pigments into the final finish, or to prevent wood stain from blotching. Lightly tinted shellac preparations are also sold as paint primer.
As it is edible, shellac was used as a glazing agent on pills or candies such as M&M's. For this purpose, it has the food additive E number E904.
Shellac was also used in the production of gramophone records until ca. 1950. See gramophone record for details.
It is now considered obsolete as a moulding compound, having very few applications.
See also
Categories: Waxes | Polymers | Woodworking | Food additives | Resins
