Lacquer is a glossy coating applied to furniture, musical instruments and other items to protect them and also to provide an attractive high-gloss finish. Nitrocellulose lacquers were once prevalent, but these were superseded by acrylic lacquers, according to Vintage Guitars Info, home.provide.net/~cfh.
The practice of lacquering objects to protect and decorate them originated in Asia. This process used the sap of the Rhus vernicifera tree. It was lengthy and complicated, with each layer requiring a long drying time. During World War II, new fast drying lacquers were developed, according to the Encyclopedia Brittanica.
Nitrocellulose lacquer uses nitrocellulose (sometimes mixed with other resins). This is dissolved in a solvent; often acetone although toluene, xylene, naphtha, or ketones are also used. Acrylic lacquers replace the nitrocellulose with acrylic.
The principle disadvantage of nitrocellulose are that it is more liable to oxidation than acrylic. This means that it tends to turn yellow over time. It is also more unstable, tending to break down with age. Modern acrylic varnishes do not yellow as much and also are more stable over time.