applying a "light dusting" with an airbrush

The key to "dusting" and "fading" with the airbrush really doesn't have much to do with making the paint "thinner". The result will be just the opposite, as you have pointed out. The key is keeping the airbrush at about 6 to 8 inches from the model and keep it MOVING. Make several passes at the extended range, and I too would use an acrylic, such as Tamiya buff. Move the brush over the work in fast swipes, applying layers until you get the level of fading that you want. Since you are painting in a less than ideal environment, why not give up on the airbrush altogether and go for MIG pigments, they are designed just for the purpose you desire and are great products, you can apply all the dust you want with an old paintbrush.

Like this sprayed with a "buff" acrylic mixture at about 15 psi.;

Do you use acrylic or enamel? I use the acrylic and it isn't nasty at all. The thinner seems to be some derivative of rubbing alcohol, but less stinky

all good ideas. i try to avoid thinner for 2 reasons: first it's nasty stuff, i paint in my bathroom and having to clean the brush out with windex is bad enough. second, i'm afraid thinning the paint too much will produce a wash which will accumulate in the recesses and such.

could holding the brush far away from the surface and letting the paint drift down cause a fine "chunking" of the paint?

what I would do, is go outside and hold the airbrush up high and pointig at the model, and then spray a thin mist. most of the paint wil be somewhere else than the model by the time it reaches it, so it will create that dust look

Have you tried adjusting thinner ratios and or air pressure?
I sometimes thin the paint 70/30 thinner to paint.
Depending on how bad the "fine spots" are you might be able to cover some of that with some pastel chalks. In other words, apply the chalks over the paint after it dries and try to blend in the dust with the rest of the paint job.
Joe

Some apply a 'light dusting' by holding the air-brush several feet away from the model and letting the paint drift down on to whatever is being painted. Some paint may dry before ever landing though. This technique may or may not be what you were looking for.

Glenn

Investing in a good air compressor would be a good idea, but to keep ut cheap, try submerging the air can in warm water and then mix the paint with acrylic thinner instead of water (if MM- their thinner, if Tamiya, their thinner, etc.) Just a couple ideas