Sometimes when applying the final varnish on a miniature, it ends up going opaque / frosting. What causes this to happen, and how can it be prevented? I have seen this occur with both Vallejo and Liquitex gloss varnish, while using a brush to apply.
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.