What causes frosting when applying a varnish?
What system are you using? Airbrush or bottle spray?


I have experienced a lot of frosting when applying varnish in humid environments. 
I have observed more frosting with spray bottles compared to airbrush (I dilute the varnish for airbrushing with Vallejo airbrush thinner).
Only apply a very thin layer of varnish at a time. I have observed frosting when I put too much varnish at once, especially with spray bottles. If more is needed, several thin layers may be applied.