Airbrushing is one of the tools at the gateway to advanced modeling. However, many of us who have never experimented with using an airbrush look at it as a skill shrouded in mystery, requiring some innate talent and/or voodoo. Nothing could be further from the truth, particularly for the painting most model railroaders do, with single (or maybe two) colors with minimal masking and no real embellishments (if you really want to be impressed, look at some of the World War II aircraft schemes, including Luftwaffe schemes with various blotches/mottling or the Italian scheme with green “smoke ring” camouflage - link to decal for the less adventurous who don’t want to airbrush these devils, but illustrates what military modelers can do!) For what we as railroad modelers do it is simply a matter of spraying paint.
First, the intent of this post is to recommend a quality, but reasonably priced airbrush. I own and use an Iwata Medea N4500 Neo Gravity Feed airbrush. New ones can be found on eBay for approximately $50. It is extremely well-made and uses metal parts rather than plastic (an important consideration for me). It is a “double action” airbrush, meaning that the “trigger” controls both air and paint flow. This is a little more complicated than a single action airbrush, but I started using a double action airbrush when I was 10 years old and never felt like it was too difficult. I am certain you can learn to use it easily too. The one other thing I will say that is attractive to me about this model is that it disassembles easily, allowing the entire mechanism to be cleaned hassle-free. This is important because airbrush longevity and smooth operation requires a good cleaning regimen after each use. It takes only a few moments, but the impacts on operation are worth the diligence. One note: I have owned more expensive airbrushes, including the Iwata Revolution and Eclipse models and they are more difficult to clean and offer no advantages for the type of painting we do. My recommendation: buy the Neo and use the savings to invest in a quality airbrush compressor (buy an airbrush compressor and you won’t need earplugs because you’re trying to airbrush with that Campbell-Hausfield 100 HP compressor that you use to power your nail gun!)
If you’re read this far and are still curious, then take the plunge. All that’s required to learn is some paint (I recommend either Model Master acrylic or Tamiya acrylic paints,) thinner (most paints are too viscous out of the bottle; I thin these two brands using the manufacturers’ thinners at about 60% paint to 40% thinner,) an air source (I recommend this compressor,) and something to paint. To learn I suggest practicing on plain sheets of 0.040” white styrene. The point is to understand air pressure settings, distance from the object being painted, paint flow relative to the trigger, and how slowly or quickly to move the airbrush to avoid adding too much paint to one area at once. That’s it. I will post more in future on this topic, but it’s one of those things where it’s easier to learn by doing than reading.