Most Vallejo paint I have used is 'air brush' ready. Just to make sure with any paint, mix it with the appropriate thinner(water or alcohol in this case) so that it is the consistancy of 2% milk. I have just painted some box cars last week using the Vallejo/Microlux paints, and they were fine right out of the bottle.
Dullcote - I have not used it in years. I just do not like the heavy spray pressure. Some friends use it all the time, and get good results. I have a friend who models BNSF, and uses some type of Krylon red/brown(Terracotta?) on his freight cars. and seals then with Dullcote - They look good.
I still have lots of Floquil/Pollyscale clear flat, and it produces a really good 'dead flat'. In the past I have had chalk weathering just 'disappear' after spraying on a flat finish. I have heard that the PanPastel line of weathering does not have this problem. I bought some, but have not tried it yet.
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin