Let's get one thing out of the way first. There is NO easy way to becoming an expert if you are not already. I will use an analogy. I am a pianist, I play very well, if I say so myself. But I can only play the piano very well because I have been doing it since I was six years old. When I was six years old, you could have sat me at the most expensive Steinway grand that money could buy, but I would still not be able to raise a tune. These days, I can play that expensive Steinway and make it sound pretty good. But I can also get a decent tune out of the beat up old upright piano at the back of the local pub.
And so it is with airbrushing. Within reason, the equipment is secondary to the skills and experience of the person using it. And it never stops. To use the piano analogy again, if I am learning to play a new piece it will sound pretty rough the first time I play it. But I persevere and eventually I can play it as well as any of the other pieces I have learnt. And I am a slightly better pianist overall as a result because now I can do something I could not do previously. And so it goes for airbrushing. I consider myself a pretty experienced individual with the airbrush, but on many projects I undertake there is something I have not attempted before, be it a particularly tricky camouflage scheme or weathering effect, and sometimes I get it right first time, sometimes I have to try several times. But in either case, I have learnt something new.
Why use an airbrush?You probably won't be reading this if you don't know the answer. Like all modellers, I started out hand brush painting everything and a perfectly decent result can be obtained for the majority of paint schemes if you are careful. But as we all know, it does not come close to the quality of an expertly air brushed model. Done well, airbrushing can give you a perfectly smooth and consistent finish, soft demarcations, intricate camouflage patterns and markings, and in conjunction with masking, near perfect hard lines as well, all of which are simply not possible with hand brushing. However hard you try, hand brushing will always leave the tell tale signs of brush marks, uneven paint thickness and trembling hands that mean your model will never look (to you at least) as good as the "professionals". These days, I only use hand brushing for small parts and details, and maybe the odd barely visible interior sections if I cannot be bothered to crack out the bottles, thinners and the other paraphernalia that goes with an airbrush session. There's no getting away from the fact that airbrushing is more hassle than hand brushing, but the results are definitely worth it.
What equipment do I need?If you are serious about becoming a competent airbrush user, it is worth investing in the right equipment - and this will cost you some money. You don't need to buy the most expensive, you will not do it justice and believe me, it is not worth the money at this stage.
Ideally, buy two airbrushes - one siphon fed and the other gravity fed (see later for explanation). There is much debate about relative merits which you can read for yourself, but personally I use the siphon fed one for large area coverage and the gravity fed one for small area coverage, it works out more economical on mediums, if nothing else. This is going to be sacrilege to many "experts", but I don't find any practical difference in the results that they are capable of at the level I am working. If you only want or can afford only one, go for a siphon fed. There are some "dual" capability ones out there, I've never used one personally but I am sure they may be a good compromise.
You also need a compressor. This is probably the most expensive single investment you will make. A decent compressor ensures a smooth constant flow of air. More on the compressor later. Do NOT use those compressed air cans that you can buy for this purpose - they are a waste of time.
Buy a plentiful supply of siphon bottles (and get airtight screw lids for them as well), paint mixing jars, pipettes, thinners for your chosen paint type, disposable face masks, and airbrush cleaning solution. Treat all of these as consumables, you will get through them surprisingly fast.
Finally, you will need some form of painting booth and extraction system. Airbrushing without a dedicated extractor fan is plain stupid. Opening the windows is NOT sufficient. It is not just for your own health, airborne paint particles (and I know this to my cost) will, over a relatively short space of time, coat everything in the room and beyond with a fine sheen that looks like dust but will not wipe off like dust! Most people make their own paint booths/extractors perfectly successfully out of old fans, tumble dryer hoses and boxes. Personally, I invested in a professional paint booth and knocked a hole in my wall for the extraction hose which is probably a bit extreme for most people, but then I do this for a living.
The airbrush.I have had a number of people recently ask whether a specific airbrush can give them results similar to something seen on one of my models. You probably know what's coming next. As long as it is of a reasonably quality, then probably yes, it can. But it's not the airbrush, it's the user. I am not going to recommend a specific brush or brand. Personally, I used to use Badger brushes, now I use Iwata. Not because Iwata is better, but because I got a good deal on them bundled with a compressor. Try and avoid "budget" brushes, go for a mid range brush. It should be double action and internal mix. Double action means you can control both the flow of air and paint individually as you brush. This is quite mentally challenging if you are new to it, but after a while it comes very naturally. Internal mix means the air and paint is mixed INSIDE the brush and ejected through a nozzle controlled by a needle as opposed to an external mix brush which technically should really be called a spray gun. These use the suction effect of the flow of air to pull paint out of the bottle and basically just blows it at the target. You may be able to patch up a scratch on your car using one of these, but you will not get far in the modelling world with it. Some of the cheap end units sold, misleadingly, as modelling airbrushes, are actually of this type and should be avoided at all costs since you have no control over the paint flow and they are brutal rather than delicate.
As I said, I am not going to recommend a specific model, but for reference my "go to" brushes at the moment are an Iwata HP-BCS and an Iwata HP-CS. They are both good, middle of the range brushes and I am perfectly happy with them. If you want more advice on what is available these days (I bought these a couple of years back) I can recommend getting in touch with The Airbrush Company who I have been dealing with for years and cannot recommend highly enough for sales, service and advice.
The compressor.This may be your single largest investment. As with airbrushes, you can spent a little or a lot on this, but as a general rule, make sure it is designed specifically for hobby modelling and that it incorporates an equalisation chamber, a water trap, a regulator and a pressure gauge. The cheapest compressors will have none of these and are a false economy. The equalisation chamber smooths out the flow of air from the piston in the compressor - without it the airbrush would receive pulses of air which are exactly what you DON'T want. This may be fine to inflate a tyre on your car, but good airbrushing needs a smooth and consistent flow of air to the brush. The water trap collects water that naturally condensates as the compressor squeezes the air and believe me, you don't want drops of water flying through your brush as you work on that delicate Luftwaffe mottle. The regulator allows you to control the pressure of the air coming from the compressor - sounds obvious but actually some very basic compressors don't include this. It is vital that you are able to do this as you will find that different techniques and paint mediums work best with different air pressures. The gauge allows you to actually see what the pressure is, and is very useful as you gain experience to remember what pressures work best for you in different scenarios and you can simply dial it in on the regulator using the gauge for reference. Another point not directly related to your output is the dB rating. This is, quite simply, the amount of noise the machine makes. Cheaper ones can be very noisy as they pump into the chamber and whilst in itself this makes no difference to the result, it does if like me, your best work is done late at night when the rest of the family is trying to sleep!
MaintenanceCleaning and maintaining your airbrush is paramount. Ideally, at the end of every day that you have used it, pull the airbrush to bits (make sure you note how to put it back together - experience talking there) and clean every part using airbrush cleaner or thinners. The needles also benefit from an occasional application of lubricant. I am as guilty as most modellers in ignoring this advice since it is such a pain but it will pay off. Over time, the airbrush rapidly becomes gunged up with paint residues and at best it's performance will be reduced/impaired and at worst it will refuse to operate. A clean airbrush is a joy to work with, a dirty one will drive you mad.
When taking the airbrush apart, the golden rule is don't touch the point of the needle. Not just because it will injure you, but if it becomes bent or damaged in any way your airbrush will start behaving very strangely. If this ever happens, replace the needle. It is the most sensitive and critical part of the airbrush and should be looked after carefully. When you wipe the needle, wipe towards the pointed end.
With siphon bottles, as soon as you have finished and you are sure you are not going to use that paint again, empty and clean the bottle. Otherwise the bottles get covered in old paint and the siphon tubes start to get blocked. If this happens, they are near impossible to clean out.
Paints and techniqueThis section will disappoint many of you because I am not going to give you any magic bullets. The internet is chock full of advice from modellers on how to achieve various results. They will specify precise mix ratios, air pressures, nozzle distances and so forth. By all means try them, but remember, these may have worked for the person who wrote the piece, with their paint and thinners, their airbrush, their compressor, their fingers, their experience and most importantly their idea of what a good finish looks like - it does not mean they will work for you. So experiment before you commit the paint to you prized model. So bear that in mind before you heed my tips below.
So to raise the first contentious debate - I used to use enamel paints, now I generally use acrylics. Why? Because they dry faster and can be easily cleaned up with water. End of. If you are using varnishes and other finishing products on top, there is no benefit to the arguably smoother finish of enamel paints. But don't let me sell you either way - use what you like using. Both can be airbrushed very successfully. Personally I prefer Tamiya acrylics for airbrushing, they seem to give me less clogging and spluttering problems than other brands, but that may just be the way I use them. Use what works best for you. And that is really my overriding point in this article - only you will discover what techniques and paints work well for your technique.
Be patient. Apply a thin coat, let it dry for a short while, then apply more thin coats until you have achieved the consistent coverage you want. Don't try and cover it all in one sweep. You will just end up pumping far too much paint into a single area and end up with pools and runs and splatters. All those things you took up airbrushing to get away from.
Light colours such as whites and yellows are notoriously difficult to achieve good coverage (especially on a dark base) and you have to be extra patient. You may afford yourself the luxury of a slightly thicker paint mix, which will help, but at the end of the day there is no substitute for patience and multiple thin coats. Fortunately, paint out of an airbrush tends to dry very quickly, if not instantly, on contact and so you can re-coat almost immediately, but make sure it is at least touch dry otherwise all you are doing is thickening the original coat and thus potentially causing problems.
NEVER hold the airbrush still while spraying. The paint will pool and make a right mess. Keep it moving, even on the smallest targets. Better that 95 percent of your paint misses the target and flies off into the background if the other 5 percent gives you a nice smooth finish.
For close work, e.g. mottle patterns or lines, there is again, a multitude of advice out there to achieve what is the holy grail of airbrush work - the perfect thin line. In truth, a truly clean thin line is a very hard thing to do but to get it to the stage required of most model paint schemes is less so. Contrary to popular opinion, the brush is not the main aspect of this (although a good quality one is essential). All I will say is that you should consider the physics of the thing. The paint coming out of your airbrush starts to spread once it leaves the nozzle. The higher the air pressure, the less the spread. So, the ideal thin line technique should, in theory, be very close to the model and a high pressure. But this presents its own problems. The high pressure means that it is harder to limit the amount of paint coming out and you end up with splatters. So you need to find a compromise. Personally, I up the pressure and back off the nozzle a bit - that works for me. Also, lock the paint flow position (most good airbrushes allow you to do this) to avoid having to keep your finger in precisely the same position, which is not easy. Keep it moving at a steady speed to avoid build up of spots, and again, contrary to much advice, I find a thicker paint mix generally more effective since it is less likely to pool and run. If it goes wrong keep going because the next bit of your pattern may be brilliant. You can go back later, cover up the offending bit and try again. I cannot claim to have ever done a complex mottled or lines camouflage pattern that has not involved a certain amount of re-spraying with base colour and starting again.
Oh - and if your model has more than five or six panes of canopy glass and there is a pre-cut canopy mask available for your model (Eduard tend to be the main player here), buy it. Don't argue. A few pounds/dollars/euros spent there are more than made up for in time trying to do it yourself and the result will always be better. It's not cheating, it is taking pride in your results.
In summarySo you will probably be getting the message by now that this is a skill that can only come with experience. By all means learn from the experience of others as you go, and there are some really good training courses out there as well if you are keen and the benefit of those is you get hands on experience. But don't make the mistake that I, and probably many of us, made when we first started.
I remember my first air brushed model - it was a 1/24 FW190. I thought the large scale would help and I eagerly cracked open my brand new airbrush in the anticipation that before too long I would have the perfect mottle pattern and lovely soft edged splinter on the wings that I had seen on so many models made by far better persons than me. Of course, the reality was far from that. After several frustrating hours it looked more like it had been used for target practice by a paintball team, and my soft edged splinter was a line of half dried crusty paint that looked like a Martian crater field with a number of rivers running off it. I spent days wondering what was wrong with my airbrush that it would not create the finish I was after. Surely it was faulty? At one point I considered returning it to the hobby shop that it came from (we still had them in those days). But of course there was nothing wrong with the airbrush, I cannot recall what model it was but I am sure it was perfectly adequate to the task. It was me and my naive assumption that I knew what I was doing.
So best of luck to you if you are wishing to embark down this road. My advice boils down to these simple facts: get the right tools, don't assume you can do it from the start, practice hard, use trial and plenty of error, don't get disheartened by your tragic early attempts, and it will come in time.