Hi.
I would appreciate any insight you might share. My issue is I have invested in Ammo Mig washes and would like to try them out with enamel thinner, but I don't know what gloss varnish to use before.
I've had bad experience with varnish reacting badly with various substances, so good advice would save me at leaast a week of experimenting.
I have been painting acrylics, handbrushes only. I've been using inherited Pactra acrylics gloss varnish up until now, but I was not too happy with it, so when it ran out I've purchased several different products:
1 - Humbrol Clear Gloss - acrylic
2 - Humbrol Gloss Cote - enamel
3 - Winsor & Newton Artists Glos Varnish - oil
If I applied any of these (over acrylic paint) and then proceeded to pin wash Ammo Mig Wash (enamel) with enamel thinner clean up afterwards, would that enamel thinner mess up the gloss layer or the paint beneath?

Also a bit unrelated question, with probably obvious answer, except I never used oils before. I have tried to mix my own oil wash last time, I diluted oil paint from tube with turpentine, the paint was nice and runny for first minute, then started to go dense very rapidly, soon it was more like tar than paint. Same happened when I replaced turpentine with cellulose thinner or acrylics thinner. The other thing is that paint never really dried. Two months later I can still smudge it when i run a finger across it. What did I do wrong? I have suspicions the paint is bad (manufacturer is Reeves, not a cheap set at all and seller recommended, but they are more like toothpaste than liquid and also don't quite want to dry up on their own)

Think of the varnish as a barrier to protect the paint underneath from the next stage. So the varnish needs to be the opposite of the substance used in the next stage. So if you used the enamel gloss it would be attacked by the next stage of your work in this case.

Thanks for the sound advice. I did run a test just to make sure i don't mess up. I am quite happy with my paint scheme, so I am double careful now. Predictably Gloss Cote was an utter failure, enamel thinner dissolved it, oil was ok, but I think enamel thinner has eaten into it a bit, acrylics varnish looked intact.

If you can get some Turpenoid Light in Ireland, I suggest using that for thinning oils for washes, pin washes and panel line washes. It's a synthetic turpentine which is less damaging than stronger thinners. It will also dry oils overnight. When using oils, I recommend higher quality oils like Windsor and Newton (although I've had really good luck with cheaper priced Mona Lisa oils). Turpenoid light mixed with oils will dry to a dead flat finish--so be prepared for that, you can freshen it up with an over spray of varnish if necessary.

As far as barrier materials for acrylic paints go, you can use enamels and even lacquers (Testors Dullcoat is a lacquer) over most acrylics as long as they're sprayed on lightly in successive coats--hand brushing just wont work well--it has a tendency to disturb the underlying finish too much. you can carefully use an enamel pin wash over SOME acrylics, if you are careful. experimentation is the key--try it on some scrap plastic before going on to the real thing.
VR, Russ