When it's still wet and sticky, acetone will completely dissolve it... that's what nail polish remover is, but buy a can in the paint section of the hardware store instead spending a fortune on overpriced little bottles at the drugstore. I always have some on hand when I use great stuff; when I'm done (for the moment) squirting foam, I pop out the plastic tube and immerse/swish it in the acetone to clear it. Then dip the nozzle in and swish it too... that way you can still get to the stuff that's still in the can.
After it sets... I haven't found anything short of a razor blade and sandpaper that'll get that stuff off.
It's used as a wood cleaning agent.
And correct spelling - naphtha
Naphthas are also used in other applications such as:
* (as an unprocessed component - in contrast to reforming above) in the production of petrol/motor gasoline.
* industrial solvents and cleaning fluids
* an oil painting medium
* the sole ingredient in the home cleaning fluid Energine, which has been discontinued. You can purchase this type of naphtha at any hardware store.
* an ingredient in shoe polish
* an ingredient in some lighter fluids for wick type lighters such as Zippo lighters.
* an adulterant to petrol
* a fuel for portable stoves and lanterns, sold in North America as white gas or Coleman fuel.
* historically, as a probable ingredient in Greek fire (together with grease, oil, sulfur, and naturally occurring saltpeter from the desert)
* an additive to fuel (usually kerosene) for fire spinning, fire juggling, or other fire performance equipment which creates a brighter and cleaner yet shorter burn.
* to lightly wear the finish off guitars when preparing "relic" instruments.