Airbrush Basics

An airbrush seems to be an intimidating modeling tool for many modelers. There’s often a misconception that airbrushes can’t possibly be that much better than traditional brushes or modelers just don’t know where to begin with them. There’s also a certain level of comfort with staying with what’s familiar rather than trying to move to an entirely new form of painting.

However, airbrushes are relatively simple tools, doing nothing more then combining paint with compressed air to allow the paint to be sprayed in a controlled way. All airbrushes perform this function, but there are many variations in the way airbrushes are built and therefore airbrushes perform this function in different ways.

Types of Airbrushes

Airbrush type indicates the overall level of control over air and paint flow.

Single Action Airbrushes

A single action airbrush means that the trigger of the airbrush is designed to release air and paint at the same time in a “single action” or movement.

Single action airbrushes work like a simple on/off toggle similar to a spray paint can. Pressing the trigger sprays paint and releasing it stops the flow of paint. The amount of paint that is released is controlled by turning a knob or screw on the airbrush.

Single action airbrushes are also referred to as external mix airbrushes. This is because paint and air are combined outside of the body of the airbrush as they’re sprayed onto the object you’re painting.

Double Action Airbrushes

A double action airbrush (or dual action airbrush) means that the trigger is designed to provide two separate actions — one for airflow and one for paint flow.

Pressing the trigger (up/down) release air. When the trigger in pressed down, air is flowing and when the trigger is released, air stops flowing. No paint is released by simply pressing the trigger.

The second action or movement controls the amount of paint that is introduced into the air stream. For this, the trigger is pulled back toward the rear of the airbrush. This gives a very high degree of control and the further back the trigger is pulled, the more paint is applied.

Pulling back on the trigger of a double action airbrush provides precise control over paint flow. This level of control over paint is not available on a single action airbrush.

Double action airbrushes are also referred to as internal mix airbrushes because paint and air are mixed inside of the body of the airbrush. These leave the airbrush already mixed.

Paint Feed Methods

The method of feeding paint into the airbrush indicates the volume of paint that can be held before refilling but has no impact on airbrush performance.

Siphon-fed Airbrushes

Siphon-fed airbrushes use a removable cup or jar attached to the underside of the airbrush to hold paint. Air suction pulls the paint from this container to be mixed with the flow of air.

Most siphon airbrushes support a number of different containers and most will allow you to spray directly from a paint bottle when doing large areas of the same color. Most paint containers on siphon-feed airbrushes are closed with a lid during spraying. Even though they have small air holes in the lids, they are often easier to work with because spills are less common.

Gravity-fed Airbrushes

Gravity-fed airbrushes use a cup attached to the top of the airbrush to hold paint. Paint is drawn down into the airbrush by gravity to be mixed with the airflow.

The cup on gravity-fed airbrushed is often permanently attached to the body of the airbrush and do not give the option to use larger containers. Caps are available to cover most paint cups on these types of airbrushes, but typically, paint is sprayed while the cup is uncovered. Because of this, some modelers may find it difficult to work the airbrush and keep the cup level to prevent spills.

Needles and Nozzles

Airbushes require paint and air to be mixed at an exact point in space — the mix point. To illustrate this, think about a magnifying glass that can focus sunlight into a small point of strong, focused light. In an airbrush, a tapered needle is used like the magnifying glass to direct the flow of air and paint to a small, focused mixing point, creating a controlled, combined flow from that point forward. 

Depending on the airbrush make and model, airbrush needles often come in different sizes, such as fine, medium or thick.  The finer the needle size, the smaller paint output; the thicker the needle, the wider the paint output. You can think of a standard spray paint can as a very thick needle. For modeling, a medium needle will often work for most needs.  Some airbrush models use what are known as “universal” needles, capable of working as a fine to thick needle depending on how they’re set.

The airbrush nozzle surrounds the needle at the head of the airbrush and has a hole for the needle to pass through. The nozzle’s opening is tapered to match the taper of the needle. As the needle is moved toward the hole, the area of the opening is reduced, reducing the paint flow. As the needled is moved away from the hole, the opening is wider so more paint is applied.

The needle passes through the nozzle at the tip of the airbrush.

As I mentioned earlier, the paint flow on a single action airbrush is controlled by a knob or screw on the airbrush.  Technically, this is because the screw changes the distance of the needle tip from the nozzle opening. This distance, and therefore the paint flow, remains constant until the airbrush user manually changes it.

On a double action airbrush, the needle is connected to the trigger. As the trigger is pulled back, as is the needle, widening the  nozzle opening and increasing the paint flow.  The paint flow is changed on-the-fly by simply moving the trigger forward or back.

Some airbrush models, usually inexpensive single-action models, use a needle and nozzle that are combined into one airbrush head assembly.  These work on the same principle, but use a very short needle permanently contained inside the nozzle which is often color coded to indicate the needle thickness.  Paint flow in these models is controlled by twisting the front of the nozzle to open or close the opening rather than moving the needle itself.  Some airbrushers using this type of airbrush may not even realize that the twistable nozzle they’re using contains a needle.

Air Flow

Airbrushes use a compressed flow of air that is fed into the airbrush through a hose. There are a number of different methods of supplying compressed air into the airbrush, including:

• Squeezing air from an tire inner tube
• Compressed aerosol can
• Air tank
• Air compressor (without air holding tank)
• Air compressor, oil-lubbed (with holding tank)
• Air compressor, oil-free (wth holding taking)
• Pancake compressor
• CO2 tank

Each of these methods has its own unique pros and cons and have more variety to explain than the airbrush itself. Therefore, I would recommend working with your local hobby store to find the air source that’s best suited for you and the airbrush you choose.

However, I would highly recommend using some form of an air compressor and steer clear of inner tubes or canned air, regardless of what you may read elsewhere. Canned air may seem like a good option but they run out of so quickly that they become more expensive over time. Not to mention, they’ll become frustrating when you waste an entire can of air trying to clear a paint clog and don’t get a drop of paint on your model.

My Personal Airbrush and Compressor Setup

I have used several airbrushes over the years and I’ve finally found an airbrush that I am completely content with.

I use a Badger 155 “Anthem” which is a double action, siphon-fed airbrush. It uses a universal needle and is in my opinion is a really good airbrush for beginner or experienced airbrush users. The Badger 155 uses both paint jar or quick-change paint cups.

For airflow, I use a simple air compressor without a holding tank. I bought mine years ago and I have never had an issue with pressure, moisture or other air flow pitfalls that I’ve read about with other air sources. My compressor is a W.R. Brown “Speedy”.

Airbrush Benefits

The biggest benefit to an airbrush is that paint can be applied in much thinner, more even coats than would be possible with a spray can or paint brush.  When airbrushing a styrene kit for example, it feels much more like you’re changing the color of the plastic than covering the plastic with paint. Alternatively, airbrushes are also capable of varied thickness of coats when necessary.

Because of the thin application of paint and control over coats, there are things that can only be truly accomplished with an airbrush. For example, I often spray a very light mist of Polyscale “Dirt” along the bottom edges of a structure to simulate dirt splashed up during years of rain.

Airbrushes can be easily used for this type of weathering, including faded signage, exhaust marks and obviously dirt. Some modelers even mist their models with Grimy Black as a final weathering step as an alternative to India Ink and alcohol. Thin application also makes them ideal for photo etched brass parts and painting tires or rail.

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About the Author

Frank Giacobbe — Co-founder of N Scale Limited, Frank has been building models since childhood and modeling in N scale since 2oo3. He is the former author of the blog, N Scale Modeling and a member of the Riverside Historic Society in Riverside, NJ. Frank has a passion for big city modeling, the 1940s and the Pennsylvania Railroad.