Shellac
Shellac is a natural, alcohol-soluble, flammable resin (based on laccaic acid) that is made from deposits on tree twigs left by the lac insect in southern Asia and India. Shellac has been known in Asia for nearly 4000 years. It was introduced to Europe about 300 years ago, and was described in The Plictho , published in 1540 in Venice. The word shellac is most probably derived from the Indian word laksha (one hundred thousand).
Shellac is the only commercially used natural resin of animal origin and it is quite different from all other natural resins. Lac, a resinous substance secreted by the lac insect (such species as Lakshadia chimensis , Lakshadia communis, Kerria lacca, Tacchardia lacca, or Coccus lacca) is collected from the twigs and young branches of certain trees in southern Asia, including fig species in northern India.
Lac females produce the resinous secretion as a protective coating for their larvae. This substance, known as sticklac or seedlac, forms a hard, resinous layer on branches and twigs. After collecting and crushing this sticklac, the resin and wood are separated by mechanical means. The remaining resin is ground, washed, and finally dried. After further treatment, the material is drawn into thin sheets of finished shellac.
In the nineteenth century and early twentieth century, shellac found use in Europe and the United States (records of shellac's use there appear as early as 1815 in The Dyer's Companion) as a wood polish for music instruments and furniture, and later in antifouling paints for ships, phonograph records, wood and wallpaper paints, printing inks, resins for electrical applications, floor polishes, fireworks, sealing wax, etc. Over the years the use of shellac in some of these applications disappeared.
By the 1850s, photography had gained considerable popularity. Early photograhs were presented in a folding case, which cast a shadow over the image and enhanced its appearance. In the United States, the case was made of tooled wood covered with a composition of shellac reinforced with wood flour. The shellac coating allowed fine detail to be reproduced; this ability to reproduce fine detail was the principal reason that shellac was used in 78 r.p.m. gramophone records until after the Second World War.
At the turn of the century, Leo Hendrik Baekeland (1863-1944) was searching for a solvent to substitute for shellac in bonding mica in electrical apparatuses when he discovered the first commercial phenol-formaledhyde resin (Bakelite).
Modern applications for shellac have included coatings for fruits and vegetables, food and confections, pills, tablets, and vitamins in the pharmaceutical industry. Shellac continues to be used in woodcoatings, printing inks, leather finishes, and stone polishing. There has been renewed interest in shellac resins for waterbased coatings and water-based printing inks as people become aware of the environment and the toxicity of chemical raw materials. Even after 4,000 years of recorded use, shellac's nontoxic and physiologically harmless characteristics as well as its watersolubility, biodegradability, film-forming properties, excellent adhesion, hardness, high gloss, superior electrical properties, compatibility with other resins, and crosslinking properties continue to suggest new applications.
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