So, just to premise:
I didn't spray Dullcote outside in high humidity, it was actually in a dry, interior room of 65 degrees that I ventilated to the outside as soon as I sprayed.
I didn't spray too close to the model or spray too much on in one coat.
Over the past six months I've used Dullcote on a handful of larger models. I don't use spray varnish on smaller models, I always use brush on.
When I used the Dullcote on two large Stars Wars Legion models it coated the model perfectly. When I used it on a large resin model it coated perfectly.
But then I recently used it on a large plastic model that I had base coated in Army Painter Blue spray. This time the Dullcote left a kind of indirect silvery, grainy finish. Now it's not like it ruins the model. It doesn't discolor the model at all or cover the color. It's more a texture on the surface that when it's in certain angles of light really shows up. Under other types of light it can't be seen much at all.
The ONLY difference this time from the other times that it was done over Army Painter sray. Army Painter sprays tend to leave a grainier finish than a GW spray or a Testors spray, etc. I'm wondering if what I'm seeing is simply the Dullcote attaching to the grainy finish of the base coat. Hard to tell!
Final thing is that I used the exact same can of Dullcote to spray several other GW plastics models within a few days of doing the other one – however those were based coated in a GW blue spray. The grainy texturing did sort of happen over the GW spray, but MUCH LESSER. I know that Dullcote will leave a very slight, very slight texture to the finish but it's very slight.
Any way this is one of the reason why I only resort to spray varnishes on larger models where brush on isn't feasible. I've just had too many weird problems with them over the years.
