I discovered I have an external mix brush.  It was part of a package where I got a compressor and 3 airbrushes.  I didn't know what it was for or how to use it until I read this column and saw the suggestion to use it for resolene. 
Sure enough, 30 seconds after I started using it, it was clogged. Aaaarrrrrggg!  I back flushed it by holding my finger over the tip.  Lots of nasty semi-hard stuff was flushed back into the bottle.  After a few times, it was working again.  Now this is a really cheap piece of c*#p.  I guess it is only $10 tops.  I found I could regulate the flow.  At lower flows, it didn't spray.  At the lowest setting it would spray, it was too strong.  I was able to do it only by spraying bursts.  I'll continue you playing with it.  If I get it to work right, perhaps I'll report.  I was really excited to think I could use the air brush to spray resolene. hmmm.