If you type Shellack into Wikipedia you are redirected to shellac:
Shellac is a resin secreted by the female lac bug, on trees in the forests of India and Thailand. It is processed and sold as dry flakes (pictured at right), which are dissolved in denatured alcohol to make liquid shellac, which is used as a brush-on colorant, food glaze and wood finish. Shellac functions as a tough all-natural primer, sanding sealant, tannin-blocker, odor-blocker, stain, and high-gloss varnish. Shellac was once used in electrical applications as it possesses good insulation qualities and it seals out moisture. Gramophone (or phonograph) discs were also made of it during the pre-1950s, 78-rpm recording era.Shellac is often the only historically appropriate finish for early 20th-century hardwood floors, and wooden wall and ceiling paneling.From the time it replaced oil and wax finishes in the 19th century, shellac was the dominant wood finish in the western world until it was replaced by nitrocellulose lacquer in the 1920s and 1930s.
Meanwhile, my dictionary of word origins, after giving the history of the word “shell” says that Shellack is a:
…compound of shell and lac ‘lacquer varnish’ (a word of Sanskrit origin, of which lacquer is a derivative), and is a direct translation of French laque en ecailles ‘lac (melted) in thin plates.’