I've heard that you can airbrush pigments. If so, how do you do it? I'm wanting to add a "Dust" effect to a completed Sherman (Firefly). Any helpful advice would be greatly appreciated. Thanks guys.

You could try and thin the pigments down with thinners first,but don't use a good airbrush if you have an old one try that first.

Don't know about pigments but I use either heavily thinned Tamiya earth brown or buff airbrushed more heavily on the lower areas and a light coat over all over the rest. Trick is to use very light coats and build it up gradually so as not to entirely cover the base coat. Patience and practice. Hope this helps.

I do with vallejo pigments diluted with alcohol (I tried different solvants, alcohol is the best imho) with really good results.

I made with dust form AK and the result is fine.

Make nice mix with White spirt and, after task, clean air brush ASAP