Safe Answer: You shouldn’t.
Unsafe Answer: Thoroughly clean the airbrush between different paint types.
If you avoid spraying different kinds of paint (i.e. oils, acrylics, uros, alcohols, keytones) you avoid ALL possibility of cross contamination.
Cross contamination can result in some complicated paint chemistry and adhesion problems. If you do encounter problems they’ll be inconsistent which are VERY hard to track down and correct.
Thoroughly clean the airbrush between paint types. This removes the residual paint and minimizes the chances of cross contamination.
By “thoroughly clean” I mean break the airbrush down and clean it out.
Which route should you take? It really depends on your circumstances. I tend to choose safe routes over unsafe routes, but I also have access to a lot of equipment.
I’ll boil it down to a couple of factors.
If you’re practicing, the finished product’s durability isn’t the question. It’s all about you developing and honing your skills.
If you’re refinishing a customer’s car the paint job needs to last. The paint job is far more important.
Maintaining a second, or even third set of airbrushes and spray guns gets expensive quickly.
Remember that reputation is more important than cash. Don’t screw a customer by cutting legitimate costs.
Professionals should suck it up and not take the chance.
Amateurs shouldn’t worry about this except to give their airbrushes a good, thorough cleaning.
I’ll take flak for this answer, but I don’t mind. Just like my first concern on this website is to give you good information, I assume that your first concern, as a professional, is taking care of your own customers.
In the end it comes down to you and what kind of quality product you wish to turn out. I also understand the cost constraints, sometimes you don’t have a choice, but most of the time you do. And for the record, there’s nothing wrong with being an amateur, it just means that you like painting things, so paint away!
I, of course have one opinion, but that doesn’t mean that I haven’t picked up some good tips for those who choose to go other directions!
This one comes from my friend Dale Robert Lampman, who describes himself as
“a personal friend who happens to be an extremely intelligent, YOUNG, witty, handsome, and greatly experienced airbrusher of immeasurable repute”.
I’ll certainly vouch for the last two.
One of the reasons I use a denatured alcohol as a final rinse is to cause any water to be sprayed out IMMEDIATELY. Water and alcohol mix easily and well. I (ahem) can’t recall how or when I learned that, but I do know it to be true. When coming from solvent (or oil) based paints, the alcohol again blends with that where water will not. That being the case, I often switch between the two (or three) kinds of paint with the same brush -all in the same day.
I researched his claim. He’s right!
Alcohol and water like to mix with one another. There’s an excellent explanation from the Ask a Scientist program through the US Department of Energy over here. However, if you’re looking for the perfect alcohol-water drink mix, you might want to not worry about it.