With a quick cleaning, wipe on / wipe off, it is rather safe. I've done plenty of tests of prolonged exposure, and never found a hint of reaction or softening.Ī word of caution should be given about mineral spirits however. I'm not sure what may have happened there, as pure VM&P naphtha just doesn't react with a fully cured nitrocellulose finish. Use it for thinning or softening paints, but not for cleaning. Acetone is basically a simple ketone, but lacquer thinners are generally a mixture of a number of solvents, ranging from acetone, methyl ethyl ketones, ethylene glycols, alcohols, xylenes, toulenes, and all sorts of other nasty stuff. These are not petroleum distillates, and are much more aggressive solvents. Some cured paints like polyesters are safe to use acetone on, but others like polyurethane, acrylic, or nitro are not. They are very strong solvents, and should not be used around plastics or cured paints unless you intentionally want to soften them. Things like lacquer thinner and acetone are in an entirely different category. White gas used in camp stoves is another close relative, and kerosene isn't that distant either. Neither will react with most cured finishes, nor will they swell wood, and are perfectly safe to use for cleaning guitars (with proper ventilation and fire safety precautions of course). Naphtha has a lower flash point, and evaporates a bit more quickly.

Both are petroleum distillates with slightly different pentane, heptane, octane, etc, levels. Naphtha is a very close relative of mineral spirits, and can also be described by some as paint thinner.

Paint thinner and mineral spirits are usually just different terms for the same thing. That's a pretty good summary from Fogleg.

Mineral spirits vs denatured alcohol