Anyone curious on how to airbrush craft or artist acrylic paints might be interested in the tirade below - if you're not, it will be pointless. I've spent years dabbling in the subject and have been advised by Golden Paints on the subject - and they know everything about acrylics. (They can claim to have invented them.) Forewarned.
Craft paints in my experience are not created equal. They vary in pigment load and general quality of the binder - so if two brands are there, plunge for the more expensive one. The one thing you can count on is that craft paints will be water based acrylics. Check the label - if it says "nontoxic" and "nonflammable" - it's water based. (If the label says nothing it will be water based. Law requires "flammable" and "toxic" materials to be labeled. If you bottle says either, it will be an "acrylic/lacquer" like Tamiya or Gunze. The only claim these brands have to "acrylic" is that you can clean them with water. They act very differently at every step and are excellent for airbrushing but bad for hand painting. That said, some people like water based paints for health reasons - I do not think the acrylic lacquers are dangerous if used properly. I use solvents for cleaning my airbrush, but stick to water based paints out of preference.) People that make craft paints want to sell it to schools - and if your pupils might drink the stuff, you want it to be pretty benign. (I'd guess craft paints might also not use extremely useful but not very healthy pigments like zinc.)
Craft paints are widely available and that's a real plus. If you're lucky enough to live where there is an art supply store (Blick Arts is the biggest in the US) or buying enough stuff to justify an internet buy there's a really good alternative. Blick arts sells the artist version of Vallejo paints. Vallejo started as an artist supply company and only branched into model paints later. (Check their website - it starts with a kind of portal - art or model.) Vallejo "Fluid Acrylics" are identical to Vallejo "Model Color" or "Panzer Aces" and thus thicker than Vallejo "Model Air." Standard pigments go for about $5 for a 4 ounce bottle - ritzy mixing pigments are more, but you'd never find those in modeling sites. That's about half the price of Golden Fluids which are made by the top US artist acrylic company. Blick also has proprietary acrylic fluids that are about the same - I like their "matte acrylics" for hand painting. These will be better paints than craft paints. How much better depends on the quality of the craft paint.
You can airbrush craft and thick water acrylics. If you want good results you need to understand a little how water based acrylics work. (Check a very good YouTube video called "Worst Mistake Acrylic Painters Make" for details.) Water based acrylics are pigments suspended in a binder made by some form of polymer. How thick the binder is will depend upon the purpose of the paint. As craft and many artist acrylics are made for hand brushing (ditto for Vallejo Model Color/Panzer Aces) they'll be fairly thick, which allows them to adhere well and quickly to non-porous surfaces - like plastic. If you thin the polymer heavily with water (I'd say anything over 20% is a risk - 50% won't work) it will go through an airbrush, but when the paint dries the binder molecules (the stuff that makes the paint film adhere) won't be able to reform and the surface will be unstable and probably look bad. A lot of home brew thinners are used - the Future/water is common. It sort of works because Future is very close chemically to a polymer - that's why it's used so commonly by modelers. So your 50/50 Future/Water means you're thinning the paint with 25% water and 25% sort-of polymer. Dried Future will hold the paint film, although I wouln't praise the finish. You will get a gloss finish obviously, but varnish will handle that. This is a good home brew, and easily available. (A usually good modeler on YouTube claims you can airbrush Vallejo Model Color with "retarder medium" which is one bad idea in my book. The stuff is a conditioned polymer, but I'd worry about the finish drying properly. Retarder can be very helpful - in drops - not dollops. The best natural retarder is glycerin - cheap, and really effective - unfortunately your paint may never dry if you use two drops.)
A better solution is to run down a bottle of "Airbrush Medium" which is made by several art companies - Liqutex and Golden are two. Very similar is something Vallejo called "Thinner Medium". They all look the same and will all work. They're white, water-like consistency and simply a thinned polymer that's the same as your paint. So this will go through the airbrush nicely and the pigments will bind perfectly when dry. However, you are cutting the pigment load with thinned paints (that's true regardless of what type of paint you use - this effect is very desireable for many applications) so don't expect the paint to be quite the same color - but it will be close. Mix it about 1:1 with craft or fluid acrylics - or less depending upon your airbrush. You might want to track down some Fluid Retarder and use a bit to avoid tip dry - just follow the instructions. All of this stuff can be found on Amazon, but the Blick web site will sell it for less. (I wouldn't experiment with flow improvers made for latex like Floetrol - the stuff is very cheap, but latex and modeling acrylics aren't really quite the same animal. But it's all water solable so who knows?)
If you want to know how acrylic paints work Golden has a splendid web site that's filled with information of all kinds. Artists are good customers and very picky. And there are also more of them. Model makers pay extreme premiums for the things we use - Golden High Flow acrylics are cheaper per volume than any modeling brand. Vallejo makes super acrylic varnishes and they're a third the price on Blick than from a modeling site.
Eric