True Earth’s FILTER & WASH are extremely thin and easy, and are simply fantastic over those models like aircrafts, where we need the maximum finesse and delicacy .
For this task you can use them thinned with simple water or water+denaturated alcohol/ethanol. And unless being not acrylics, they can also be thinned with many acrylic paint thinners. Best surfaces for airbrushing are matt.
Proportionally fit the air pressure in function of the density of the filter. (Less dilution = higher pressure).
AIRBRUSHING THE WHOLE MODEL
Thinning as you like and airbrush.
SMALL SPOTS AND THIN LINES AIRBRUSHING
For airbrushing Filter & Wash over little areas, or very thin lines, fit a higher pressure, ab. 22 to 27 psi - 1,5 to 1,8 atm. Airbrush nozzles ranging from 0,15 to 0,2mm. The best way to avoid any excess, is to work slightly in backlight, to see the wet reflection sprayed on the model, instead of expecting an immediate color change, as it would be for a paint.
Remind that they are not paints. They work in transparency and are not designed to cover. Then you spray only minimal amounts on the area. Let it dry, check result and if needed add a next layer, working in progressive steps.
Aibrush cleaning is unequalled ! Just some drops of water are enough for a clean tool, because the all- resin formulation flows away without adhering to the airbrush.