ABC's of AirBrushing Model Trains

Experienced modelers will tell you that the only way to consistently produce high-quality, scale finishes on your models is to use an airbrush. Scan the articles in any issue of Model Railroader and you’ll find the majority (if not all) of the models were painted with an airbrush. Asking around at a club meeting or a model contest will yield the same result.

With this kind of overwhelming endorsement, deciding to buy an airbrush often takes little time. Learning to use one, however, can seem to take forever. Despite its simple looks, an airbrush can be maddeningly frustrating the first few times you try to use it. Don’t give up. Whether you’re considering buying your first airbrush or are reluctant to use one you already have, we’ll help you get started.

Your airbrush is a miniature spray gun — compressed air blows over the paint nozzle, creating a suction that draws paint from the color cup or siphon jar. The paint flows out into the air stream, breaks into fine droplets, and flies to the model’s surface. The paint nozzle controls the amount of paint that’s released, and the airflow is adjustable. The paint pattern can be adjusted from several inches in diameter down to 1/16" or less.

Airbrushes come in two categories: single-action and double-action. On a single-action brush, the trigger button controls only the airflow through the airbrush. Paint flow is controlled separately by an adjustable paint nozzle.

Most modelers start with single-action airbrushes. They’re inexpensive (prices start around $45), have fewer parts, are easy to clean, and can tackle most general painting tasks. Their only shortcoming is their limited ability to paint fine lines. The paint nozzle on most single-action brushes meets the airflow at an angle. The air travels out of the brush and across the tip of the adjustable paint nozzle. Although this design is simple and works well for most painting tasks, it doesn’t produce fine lines as well as a double-action brush.

On double-action airbrushes, the trigger controls both the airflow and paint supply, allowing for greater control and flexibility. Pushing the trigger button down opens the air valve, and pulling it back increases the paint flow.

The paint nozzle and air nozzle of a double-action airbrush are parallel. The air flows around the end of the paint nozzle, and the paint needle’s position within the nozzle controls the amount of paint that’s released. Double-action airbrushes allow for finer lines and more efficient operation, but are more expensive (starting around $70), more complicated, and more difficult to clean.

One of the most important steps in selecting an airbrush is to think about what kind of painting you plan to do. The most expensive or complicated airbrush isn’t always the best choice. Attend a club meeting or model contest and ask other modelers what airbrush they use and what model they would recommend. Most will be happy to steer you toward an airbrush that will be right for your needs.

All airbrushes are powered by compressed gas — usually air. You’ll want to have 15 to 30 pounds per square inch (psi) at the airbrush to handle most hobby paints.

Many single-action airbrush starter kits come with a can of propellant and a regulator. Propellant cans hold 6-15 oz. of propellant, enough for one or two medium-size models. Propellant cans are silent, but are difficult to regulate, and at $7 to $12 each, they get expensive in a hurry. If you plan to airbrush regularly, invest in a compressor or another source of air.

Many modelers opt for simple electric piston or diaphragm air compressors. They’re affordable (starting around $150), but can be noisy, and many don’t allow you to adjust the air pressure.

More advanced compressors have built-in reservoir tanks. The compressor turns on to recharge the tank when the pressure drops below a certain level.

Adding a moisture trap between the compressor and the airbrush is a good idea. As compressors operate, they condense water vapor in the air. The water trap removes moisture from the air supply before it finds its way through the airbrush and ruins your paint job.

A number of modelers have chosen carbon dioxide (C02) or nitrogen tanks as an alternative to air compressors. Normally used to power fountain-drink dispensers, carbon dioxide tanks are available from compressed-gas dealers. Nitrogen tanks are available from most welding-supply dealers. Both offer silent operation and are easily regulated. Also, you won’t need a moisture trap with either system. A 20-pound tank with a regulator can cost between $150 and $200, and will hold enough gas to paint 15 to 20 average models. Recharging the empty tank will cost $10 to $20.

Because of the high pressures within, both carbon dioxide and nitrogen tanks must be handled carefully. Your local compressed-gas dealer will tell you what kind of regulator you’ll need, show you how to handle and store the tank safely, and let you know how often you should have it inspected and pressure tested.

Some modelers have added regulators to low-pressure hardware-store air tanks normally used for filling car tires. A five-gallon tank filled to 100 pounds of pressure will provide for 5 to 10 minutes of continuous spraying, enough for one or two small models. Low-pressure tanks can be an affordable alternative to other air sources, particularly if you only plan to airbrush occasionally, but you’ll still need to find an air source to fill the tank.

An airbrush is a remarkably adaptable piece of equipment; you can use it to apply almost any type of paint, from enamels, to lacquers, to acrylics.

No matter what type of paint you choose, however, it will need to be properly prepared for use in an airbrush. The first step is to make sure the paint is thoroughly mixed. Stir the paint until all of the pigment on the bottom of the bottle is mixed in with the carrier at the top.

Almost all hobby paints need to be thinned to spray properly through an airbrush. Thinned paint goes bad eventually, so only thin as much as you’ll need for your painting session. Never thin paint in the bottle; transfer it to a separate container, and use the thinner recommended by the paint manufacturer.

There aren’t any hard-and-fast ratios for thinning paint for airbrushing. Thinning the paint to the consistency of milk is a good starting point, but experiment to determine what ratio is best for you, and for the brand and type of paint you’re using. If you add too much thinner, the paint won’t cover properly, and if you don’t use enough, the paint won’t spray properly — or at all.

Generally, gloss paints require more thinner than flats. Some paints, such as Testor Metalizer, don’t need to be thinned, and can be poured straight from the bottle into the airbrush. Read the manufacturer’s directions, and experiment on an unwanted practice model.

By far the best way to learn how to airbrush is by doing it — thin some paint, fill the airbrush, point it at a model, and press the trigger.

As the paint leaves the airbrush, it forms a cone-shaped spray pattern, with its point at the tip of the airbrush. The size of the spray pattern increases as the distance between the airbrush and the model increases.

For general painting, such as applying an overall base coat, you’ll want to use 15 to 20 psi of air pressure, and hold the airbrush 3" to 6" from the model. If the airbrush is too close, the paint will run, and if it’s too far away, the paint will dry on the way to the model and won’t adhere properly.

Practice making smooth, even strokes with the airbrush and begin and end each stroke off the model. If you don’t, the coat of paint will be thicker at the ends and uneven.

The paint should land on the model’s surface still wet. With flat paints, the paint will hit the surface and look slightly shiny for a few seconds.

Once you’ve mastered basic paint application, you’re ready to move on to more advanced techniques. Holding the airbrush at a 90-degree angle to the model produces a round, even spray pattern with a fuzzy edge. However, tilting the airbrush 45 degrees and holding it closer to the model produces an elliptical spray pattern, where the edge nearest the airbrush is sharp and the edge farthest away is less distinct. Mastering the elliptical spray pattern is the key to airbrushing complex paint schemes.

With a little practice and some airbrush adjustments, you’ll be able to duplicate a feathered edge on your models. By holding the airbrush close to the model and angling the tip, you can paint the feathered edge using the sharper edge of the spray pattern. Mastering this technique takes plenty of practice, but the results can be spectacular.

A guitar is a simple instrument with a few strings and easy adjustments, but no one can pick one up and expect to play like Eric Clapton the first time out. An airbrush is the same way. Although it seems simple enough when you take it out of the box, it can be discouraging when your first attempts don’t turn out the way you expected. There are plenty of variables involved with airbrushing, and only with practice will all the settings and thinning ratios start to fall into place and give you the results you want.

 Because you’re going to be airbrushing models, it’s best to practice on models, instead of paper or other porous surfaces. Look around your workbench and modeling area — are there any old models you’re thinking of throwing away, or half-finished kits you’ll never get back to? Use them for practice. Learn what different thinner ratios and air-pressure settings will do. See how fine a line you can paint. Learn to paint the complex curves of a car body without the paint running. It’s the practice that counts.

Practice models also come in handy when you’re setting up the airbrush to paint your current project. Is the paint thinned properly? Do you have the correct air-pressure setting? A few passes on a practice model can point out an error.