Traditional guitar finishes include oil varnish, spirit varnish and nitrocellulose lacquer.
Nitrocellulose finish change hue with age with transparent coats go from clear to golden amber, while other colours fade and are prone to wear.
Guitar manufacturer in the early 70's started to use heavey polyester or epoxy finish 'plastic' or 'thick-skinned'. It can dampen vibration and make the guitar sound tight, choked and nasal.
Most manufacturers now use a polyurethane finish a compromise between the two.