External Mix

An external mix airbrush introduces paint into one side of the air stream.

The popular theory is that theseairbrushes mix the paint and air outside the nozzle tip.  It's true--but that definition is also true of internal mix airbrushes which also mix the paint and air out side the nozzle.

My favorite way to explain this scenario is to show you how it's done.

The Guru's Experimental Challenge

The next time you go out for fast food...

1. Order something that requires a straw to drink (no milkshakes!). 
2. Blow across the top of the straw at whomever had the unfortunate luck to say yes to this meal with you.
3. When you achieve a fine aerosol mist of your favorite beverage and deposit it upon your soon-to-not-be-friend you just demonstrated how an external mix airbrush works.
    
   The drink follows the straw up to the air stream you produce.  When the drink hits the edge of the air stream it atomizes and covers your friend.
4. I'm sure your friend will understand your inquisitive scientific nature...

The Good

• Very difficult to clog
   
  Spray chunkier paint.  Spray thicker paint.  But spray away!  There's not much to get in the way unless you're using amazingly thick, chunky paint, like house paint!
• Easy to clean
   
  Pipe cleaners or small bottle brushes will generally do the job for you.
• Very forgiving of paint consistency mistakes
   
  They don't mind the thicker paints, they don't mind your mixing mistakes as much.  They still have their limits, but those limits are far greater than an internal mix airbrush.
  

The Bad

• Uneven atomization
   
  One side of the pattern tends to get more atomization than the other side.
   
  
• Uneven spray pattern
   
  The spray pattern looks like a squished O approaching a D
   
• Hard to get fine details
   
  Extra fine detail requires something to guide the paint to it's destination.  Though it's my theoretical opinion, an external mix airbrush should be capable of delivering great detail if it had a pointy needle, but the manufacturers don't have this particular combination.
  

The Guru's Opinion

Usually an internal mix airbrush trumps an external mix airbrush simply because the internal mix airbrush offers more control and better spray consistency.  However there are applications where you don't need the extra headaches that go along with more control.

If you're spraying nothing but larger areas and don't need any details, this could be the configuration for you.