Airbrush. For some, it might seem a mystical device, creating beautiful paint jobs by means of magic. For others, it’s just an indispensable tool, just like a hobby knife or sandpaper.

Although it might seem intimidating at first, there’s really nothing to fear. In this series I’ll cover everything you need to get you on your way to creating beautiful, custom painted kits. From technical information, through buying your own airbrush kit, to painting and maintenance. Hopefully by the end you’ll feel confident and ready to step into the wonderful world of painting models.

In this episode we’ll cover the technical aspects – how it works, how various types of airbrushes differ and what air sources can we use to power them.

Ready? Let’s go!

How does it work?

Before we talk about different airbrush types, let’s take a quick look on how this tool works. I’ll try to keep it simple, as we don’t need to know the exact science laws behind it.

The basic principle is creating a pressure difference. As the air passes around the nozzle, it exits the airbrush at high speed. The pressure in that area is lower than atmospheric pressure surrounding the brush. As we open the paint flow, physics (for lack of a better word) tries to equalize the pressure. In the process, the paint, pushed on by the atmospheric pressure, is sucked into this lower pressure area and, at the same time, airflow. Moving air atomizes the paint and carries it forward. 

I know it all seems abstract and confusing, so I’ll try to give you a simpler example. Think of Star Wars, or any other movie involving space travel. Pressure inside a spaceship is always higher than outside it, in the vacuum of space. Whenever a hull breach occurs, all the air, loose equipment and the crew start getting pulled outside. It’s the same principle. Now just think that air exiting the airbrush is space, airbrush itself is the spaceship and the poor crew is paint. Opening the paint flow is like a hull breach that sets it all in motion. 

Airbrush Types

Now that we have a general idea of how an airbrush works, let’s take a look at various types and how they differ from one another.

Every airbrush has three main characteristics, kinda like character traits in an RPG game. Those three are mix, action and feed. Combination of those determines what purpose particular airbrush fits best. At the end of this section we’ll also look at the different needle / nozzle sizes (the 0.2mm, 0.35mm etc. often found in the description).

Mix

First off we have mix, which determines the point where paint is introduced into the air stream.

External Mix As the name implies, external mix airbrushes combine air and paint outside the device. Usually the airbrush’ body is a simple air blower, with additional nozzle, as well as paint jar, mounted on the underside. As the air exits the airbrush, it passes around this secondary nozzle and siphons up the paint, mixing with it and propelling it forward. Overall, external mix airbrushes are the simplest, cheapest and – as far as modeling purposes go – worst performing ones. They don’t atomize paint as good as internal mix constructions, resulting in a coarser spray pattern with much bigger paint dots. They also don’t allow anywhere near as much control. External mix airbrushes are in minority nowadays, though Badger and Paasche still produce them. The cheapest ($5-$10 range) made-in-China airbrushes use external mix too. Recently, much laughed at Gundam Marker Airbrush also popped up.

Simplified schematic of external mix airbrush.

Internal Mix On the other hand we have the internal mix – while far more complicated, it’s also the superior, most popular design.  Main distinguishing feature of internal mix airbrushes is the long, extremely sharp needle going through the middle of the body, with a size-matched nozzle at the front. As the air is channeled around this nozzle and out, it siphons the paint along the needle, mixing with it as they both exit the airbrush. The amount of paint sprayed depends on how big the opening between the needle and nozzle tip is. Overall the internal mix construction allows for better atomization and far more control over the spraying than external mix. It has one major downside though – a fine point of the needle is rather fragile and easy to bend, especially when pulled out for cleaning. Once damaged, consistent spraying becomes nearly impossible and it needs to be replaced. Eventually it happens to all of us. Most modelers go through at least a few needles.

Simplified schematics of an internal mix airbrush.

Action

Another characteristic of an airbrush is its ‘action’. Although it refers to the trigger operation, what it’s truly about is the way we adjust paint flow.

Single Action In a single action airbrush, trigger can only be pressed down to control the air flow. To change the amount of paint we spray, we have to manipulate the adjustment screw. You can think of single action airbrush as finely tuned spray can. Single action can mostly be encountered in external mix airbrushes, although internal mix single action ones also exist, like the Badger’s series 200.

Adjusting air & paint flow on a single action airbrush.

Double Action As you probably guessed, in a double action airbrush, trigger performs two functions. As before, it can be pressed down to control air. In addition, by pulling it back we also move the needle, allowing more paint to pass through the nozzle. The further back we pull the trigger, the more paint we spray. It’s a construction exclusive to internal mix airbrushes. Some double action airbrushes include a small screw in the handle, which limits maximum needle movement. There is also an unique variant of double action airbrush – one with pistol trigger rather than button-like one at the top. Those operate like a spray gun. As you pull back the trigger, at first it only lets the air through. Only further back it also moves the needle, allowing the paint to flow.

Adjusting air & paint flow on a double action airbrush.

Feed

The final variable is feed – the direction from which paint is siphoned into the airbrush.

Bottom Feed Also called siphon feed, these airbrushes use paint jars mounted under the body. As the paint needs to be pulled up against the gravity, this construction requires high air pressure to operate. Bottom feed airbrush works very well for quickly covering large areas, but falls short when it comes to fine detail painting. Although they can usually use the same fine needles and nozzles as gravity feed brushes, higher pressure makes it harder to work close to the model. One of their biggest advantages is the ability to quickly change colors – simply by swapping the paint jar for another one.	Iwata HP-BCS bottom feed airbrush. With a large paint jar and 0.5mm needle, it’s perfect for quickly painting large areas.
Gravity Feed We can easily recognize this type of airbrush by a small paint cup mounted at the top. As the gravity pulls the paint down into the body of the brush, it can operate at much lower pressure than bottom feed. In addition, while the cup can usually hold 5-7ml, this type of airbrush works perfectly fine even if we only put in 2 drops of paint. All of this makes gravity feed perfect for detail painting. Don’t get the wrong idea though – it can easily spray big areas too. Overall, it’s the most versatile type.	H&S Infinity CR+ – a high end gravity feed airbrush.
Side Feed Side feed is a rather odd airbrush. It uses a rotating, side-mounted cup, which allows it to be used straight up or straight down. It’s similar to gravity feed, though it requires slightly higher pressure. Back in the day it was a tool of choice for photo retouchers. Nowadays it’s sometimes used by fine artists and car painters, as it allows them to look straight at the details they’re painting, without paint cup in the way. Some models also include a paint jar, allowing them to work like a bottom feed.	Badger Renegade R2S Spirit side feed airbrush.

Needle & Nozzle Size

Compared to the characteristics I described above, this one is kinda different.

Needle and nozzle determine how wide the spray pattern of an airbrush is. Unlike other traits though, this one is not set in stone. Gravity feed airbrush will always stay gravity feed – but we can easily replace its 0.2mm needle set with 0.4mm one. That is, of course, if manufacturer provides them.

So what do those numbers mean anyway? Basically, maximum nozzle clearance. The bigger it is, the wider spray pattern. Bigger nozzles will also let thicker paints through. Water based acrylics will flow just fine through 0.35mm nozzle, but they’ll quickly clog 0.15mm. You can force them through it, but it usually involves a lot of effort and frustration. Sizes like 0.15mm are usually used for inks, watercolors and heavily thinned lacquer paints. 0.2mm and above will let most hobby paints through without issues.

There is no one standard as far as the sizes go – H&S and Grex stick to nice, round values, while Badger and Paasche go all over the place, with sizes like 0.21, 0.31, 0.33, 0.38, 0.53, 0.66mm and so on. I know, imperial units follow no human logic. Iwata has a mix of both for whatever reason.

To give you an idea what various size ranges are good for:

As you can see, 0.20mm to 0.35mm is the most versatile range. No surprise these are the most used sets for scale modeling.

 

Finally, a very important note. When buying additional sizes, always ensure you get the entire set from the manufacturer of your airbrush. That is, the nozzle, matching size needle and, sometimes, the air cap / head assembly. Using a cheap made-in-China needle that’s not matched to nozzle can easily damage it. 

Air Sources

We discussed airbrushes, but even the most expensive one won’t power itself. For that, we need high pressure air, so let’s go over the available air sources!

Compressors

Compressor is the most common air source for an airbrush. No, I don’t mean those huge, loud ones you might have stashed in your garage. Sure, we can use those, even hook them up to big storage tanks. It’s a decent option if you have a workshop outside the house, but they’re definitely not suitable for a living room. No worries though, there is a better alternative.

Compressors we use for airbrushing are quite different. First off, they’re much smaller and easily fit on a desk. Secondly, operating at 40-50dB, they are rather quiet. Hairdryer or a vacuum cleaner make much more noise. Finally, they require no maintenance, aside from draining the tank after we’re done painting.

Air tank itself is optional, but I highly recommend it, as it prolongs the lifetime of a compressor. With it, the device only turns on when pressure in the tank falls below a certain level. Without it, the compressor works all the time and we have to turn it off every now and then, so it can cool down. Tank also serves as initial water trap.

Which brings us to the one disadvantage. As the device heats up, it also heats up the air it pumps, causing the water to condense. Nothing ruins the paint job like water in the air flow, making water traps necessary. Thankfully, each compressor of this type comes with one – built right into the pressure regulator. The tank also eliminates some of the moisture. If needed, we can add another one, often installed right under the airbrush.

You might also run across another kind of compressor – a little cube, often included in the cheapest airbrush kits. Don’t bother with those. Their output is rather low, with no way to regulate air pressure. Plus, they heat up extremely fast, and as we already know, heat equals moisture (they don’t have water traps) and breaks to cool the device down.

A proper airbrushing compressor is the best air source for 98% of people. I’ll go over other options though, mostly for completeness’ sake.

CO₂ Tanks

Tanks of compressed CO₂ are a good air source as well, but they’re rather situational. They have some advantages over the compressors, at the cost of convenience.

First off, they’re completely silent. Additionally, as they have no moving parts (aside from a regulator), there’s no heat or moisture it generates to contend with.

As far as disadvantages go – they eventually run out of gas and need to be refilled. The bigger the tank, the longer it lasts, obviously. Big ones are very unwieldy though, often requiring a hand cart to get them anywhere. Probably not a good option for anyone who lives in a building with no elevator. Sure as hell you’re not going to fit one on your desk either.

Propellant Cans

Finally, there are propellant cans. Long story short: they’re crap.

They often come with cheap, made-in-China external mix airbrushes, branded as “beginner” or “starter” set. Aside from airbrush itself being rather horrible, they’re simply bad as an air source. To begin with, you can only pack so much air in a can. Long term they’re definitely not an economical option. Kinda like using spray cans instead of an airbrush. More importantly though, they simply can’t keep a consistent pressure. From the moment you start spraying, the pressure inside the can is constantly dropping (which also happens with CO₂ tanks, but to a lesser degree).

And since there’s so little air in the can, you’ll start noticing this drop rather quickly. Probably within minutes.

To give you an idea just how bad they are – Badger sells propellant cans. But Ken Schlotfeldt, owner of the company, will be the first one to tell you to stay away from them. So… yeah.

 

That’s pretty much it for the technical stuff. In the next tutorial I’ll cover buying an airbrush kit. 

Now, to wrap up this one, let’s look at the history of airbrushes.

 

A Bit of Airbrush History

Airbrush history began in 1876. This is when Frances Edgar Stanley invented the first airbrush-like device. Basically an atomizer with adjustable material flow. Although it was an important milestone, the construction was never brought to market.

The name ‘Air Brush’ itself dates back to 1883, when Liberty Walkup applied for a patent on a first double-action airbrush. Name itself was an idea of his wife – Phoebe. Walkup’s device was a breakthrough. Unlike earlier designs, this one could be used with just one hand. It was, in fact, his second improvement on an earlier device – the ‘Paint Distributor’, created in 1879 by Abner Peeler. 

Also in 1883, Walkup started “The Rockford Manufacturing Company” to produce his new invention. Soon after it was renamed to “The AirBrush Manufacturing Company”. Later, in 1886, Walkup and his wife formed the Illinois Art School. In addition to standard curriculum, the school offered classes on airbrush painting.

Next two iterations, invented by Charles L. Burdick in 1889 and 1891 established a basis for a modern airbrush. His devices introduced a familiar, pen-like shape, which sprayed the paint forward, rather than straight down. Most importantly though, his second model introduced the internal mix. Thayer & Chandler company manufactured and further developed this design. Later on Burdick moved to London to sell his airbrush under the name ‘Aerograph’. To this day we call airbrushes ‘aerographs’ in many European countries.

The following century saw many refinements and new manufacturers. At the end of day though, modern airbrushes are still based on the concepts dating back to 19th century.