Shellac is a brittle or flaky secretion produced by the lac insect Tachardia lacca, commonly found in the rainforests of Southern Asia (e.g., Thailand). Actually, the insect's larvae settle on the branches, pierce the bark, and feed from the sap. The female insect produces a protective coating over their bodies, producing a thick incrustation over the twig. When larvae emerge, the thick incrustation is scraped off and dried to yield the stick lac, which still contains wood, lac resin, lac dye, and various organic debris. The purified product called seed lac is obtained after grinding, screening, and washing the stick lac.

Shellac is a naturally occurring polymer, and it is chemically similar to synthetic polymers. Thus, it is considered a natural plastic. It can be molded by heat and pressure methods, so it is classified as a thermoplastic. It is soluble in alkaline solutions such as ammonia, sodium borate, sodium carbonate, sodium hydroxide, and various organic solvents. When dissolved in acetone or alcohol, shellac yields a coating of superior durability.

References

[1] Materials Handbook. DOI 10.1007/978-1-84628-669-8.