nitrocellulose

I have run into a bit of a problem with this. Spray it no worries, low pressure gun around 15psi , thinned down ok etc. Goes on nice and clear but when it drys I have some white spots here and there. Cleaned the gun out several times, taken it back to bare wood a couple of times, tried it over DO, still have the white spots.



I would appreciate some feed back from learned Gentlemen of this forum as where I'm going wrong.