Shellac is scraped from the bark of the trees where the female lac bug, Kerria lacca, Order Hemiptera, Family Coccidae secretes it to form a tunnel-like tube as it traverses the branches of tree. Though these tunnels are sometimes referred to as "cocoons", they are not literally cocoons in the entomological sense. This insect is in the same family as the insect from which cochineal is obtained. The insects suck the sap of the tree and excrete "stick-lac" almost constantly. The least coloured shellac is produced when the insects feed on the kursum tree, (Schleichera trijuga). The raw shellac, which contains bark shavings and lac bug parts, is placed in canvas tubes (much like long socks) and heated over a fire. This causes the shellac to liquefy, and it seeps out of the canvas, leaving the bark and bug parts behind. The thick, sticky shellac is then dried into a flat sheet and broken into flakes, or dried into "buttons" (pucks/cakes), then bagged and sold. The end-user then crushes it into a fine powder, mixes it with ethyl alcohol prior to use to dissolve the flakes and make liquid shellac.
From:http://www.chemical-reagent.com/products/Shellac/
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