Nitro-
Cellulose
Lacquer

Nitrocellulose lacquer is an indication of a good sounding guitar. It allows the wood to vibrate and therefore, sound better. The process takes weeks to apply, as opposed to modern polyurethane lacquers that were developed in the late 60s. Poly-based lacquers, however, compress the wood and constrict the acoustic value of some of the best tone woods.