I was having a problem spraying Misson Models gloss clear coats I was using 3 drops of there thinner it was drying matt/semi -gloss I'm not sure if i was thinning it too much and I did a test on a test model and I came out glossy.
Thinning too much wouldn't have caused it to dry matt I would have thought (if anything it would stay wet longer). I'm thinking maybe more air pressure too high while spraying or it was drying before it hit the surface maybe?
I was spraying it at 15 psi I have now changed it to about 12 PSi and all so found out you need to thin it the same as the paint so was doing 50 drop of gloss coat to 15 drop of thinner now. I think the problem was I wasn't thinning it enough and getting pissed off with it.