just wanted to know any functional difference between polyurethane and nitro cellulose. i remember sumone saying that nitro was weaker? he mighta misunderstood it as what the material is made out of, because i dont think the gloss coating makes a difference. Then i could be really ****in wrong...some input from the experts?
neck finishes, I know nothing about.

body finishes however, Nitro is a "richer" finish as it is thinner, so suposely let's the wood "breathe" and it wears off a lot with time . Poly finishes tend to be looked at as cheap finishes, but they just apply a thicker coat of polyurethane.

Hell, it's pretty much the same thing
Nitrocellulose - Thin, breathable, can be sticky when new, classic finish, easily repaired, not dissimilar to wood

Polyurethane - Thicker, generally a lot slicker, harder to repair but it dosent get damaged as easily as its harder, its basically a plastic
Gibson 58 RI VOS Custombuckers
Mesa Lonestar Special 2x12
Nitrocellulose finishes can "melt" as you play them. The chemicals in your hands and sweat can break the finish down, making it sticky and eventually strip it. This takes a while and if you wipe the guitar off after playing it, it will take even longer. There's also crazing, where tiny cracks appear in the finish. As the wood expands and contracts, the finish doesn't want to go with it, so it cracks. This can be prevented or staved off by keeping the temperature and humidity stable. Sudden temperature changes can really cause some crazing.

These all take a while to manifest though and Nitro can be touched up by a luthier.
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