For whenever you need a hard, non-discolouring organic varnish. Shellac is collected from the bark of the kursum tree where the female lac bug excretes her sticky deposit. The raw shellac found mainly in India and Thailand, contains bark shavings and lac bug parts. It is placed in canvas socks and heated over a fire.
This causes the shellac to liquefy and seep out leaving the bark and bug parts behind. The thick sticky shellac is then dried into a flat sheet. When needed this is broken up and mixed with alcohol to make liquid shellac. Shellac is UV-resistant and does not darken as it ages.
Shellac gives a very hard surface and scratches less easily than lacquers and polyurethane. Damaged areas can easily be touched-up with another coat of shellac because the new coat melts itself into the existing coat. Don't buy more than you need as, being organic it has a short shelf life and should not be stored when opened.