Hi Stuart. Vallejo varnishes are for the range Model &
Model Air. They used to be marketed under both
Model Air & Model but they were the same product..
For varnish I use a .4 needle/nozzle which gives a fine finish. The varnish straight from the bottle. Tried .2 but found a few problems & hence the .4.
Problem is if you thin you will probably have to apply more coats. Not such a problem with matt but how gloss reacts I cannot say. Like to keep to as small a number of coats as every additional coat picks up another bit of stuff hanging in the air.
If you thin use Vallejo thinner. One of Vallejo paints advantages is the ability to level out & give that nice finish even if you have overloaded in an area. If you use Vallejo thinners it has similar ingredients ,spreading & adherence,to the paints. Place a good size spot of thinners on plastic leave it to dry & there you will have the remains stuck fast to the plastic.
Laurie