I know from the questions I get from time to time, that there are plenty of modelers out there, by no means beginners, who don’t understand or don’t want to try using an airbrush. It is natural to be a little hesitant about any new experience, but the airbrush should not be something to be feared.
There are situations where you can spray paint adequately with a rattle can, and I do that myself for some kinds of jobs. But the first problem is that you have to use the color that’s in the can. That can work all right if it’s something simple, like black, that you need, but for any specific railroad color, obviously not so good. And paint delivery is not really under your control — paint flow is either on or off. I know from having it happen, that a particular rattle-can nozzle can deliver a lot more paint than you had in mind just then. It can also sometimes “blort out” gobs of paint just where you don’t want them.
So an airbrush isn’t just someone’s idea of a complex way to do a simple job; it’s a solution to all the problems just described with rattle cans. You can mix the color and consistency of the paint you want to apply; and you control the rate of paint application.
You can start with something truly simple. I have used a Badger 250 brush for many years (it’s now in their catalog as a “spray gun,” that’s how primitive it is). It looks like this, though the one I have is kind of a minty green:
It’s what is called an “external mix” brush, because the compressed air passing horizontally over the paint nozzle (sticking up) draws paint out into the air stream, outside of the instrument itself. The main virtue is its simplicity; it’s a good tool to learn on, and very inexpensive to buy. This and a range of other Badger products can be found at their website (here’s a link to it: http://www.badgerairbrush.com ).
I also have, and have used very successfully, a Thayer and Chandler double-action air brush. This fine tool, available nowadays from Badger, mixes paint internally instead of externally, and has a double-acting pushbutton that you use to control both the flow of paint, and the flow of air. It can place very small amounts of paint, down to the level of shading. But for most models receiving an overall coat of paint, or overall weathering, I still use the Badger 250.
The second necessity is a source of compressed air (or other gas) to do the work. Commercial cylinders of either nitrogen or carbon dioxide are possibilities; so are commercial products in aerosol cans, such as Propel (sold by Badger). I got started airbrushing with Propel, and it worked fine. But for more than 25 years, I have used a small Badger air compressor, the Model 80-1, which is fairly noisy. If I did more painting, I would probably replace it with a “silent” compressor.
And finally, you need a spray booth or other means to pull solvent and paint fumes away from you. I began by painting out in the driveway of our home, but eventually purchased a small commercial booth (from a company no longer in existence), which was not very expensive.
With any of these tools, you need to practice to get the hang of what you are doing. Use a failed model project to work on, or maybe something like an Athearn blue box kit that you no longer plan to build. Have at it, and learn as you go.
I won’t presume to offer more instruction than that here, because there are some fine books out there, which take you through it, step by step. The best recent one, in my opinion, is this one from Kalmbach Books.
Note that it is not a model railroad book. The folks in other model-building hobbies have a lot to offer in techniques, and this is just one example. If your Local Hobby Shop only carries trains, see if you can find one that carries plastic models (airplanes, armor, autos) and they may well carry FineScale Modeler magazine and books like this one.
Here are two more books, both from Kalmbach, though only one is a model railroad book. Both provide considerable detail in a clear, understandable way.
In addition, the book I reviewed awhile back, by Tim Shackleton, also contains a nice section about airbrushing, including his comments about several commercial airbrushes which are available. You can read my post at: http://modelingthesp.blogspot.com/2014/11/an-excellent-book-on-weathering.html .
Lastly, I should mention safety. Paint solvents are not good for you, if absorbed through the skin or breathed into the lungs. Particles of paint pigment are not good for your lungs either. I always wear disposable gloves and an inexpensive dust mask, even though my spray booth pulls a pretty good flow of air through the booth and away from me. This is discussed at more length in each of the above books.
Bottom line, for me: airbrushes are a superior method of painting models, whether rolling stock or structures. And learning to use a finer-spray model will permit much better weathering and other applications. If you haven’t tried it, take the plunge, buy an inexpensive starter set (Badger has a couple of them), and have at it. I think you will find it easy and rewarding.