By Terry Miesle © 2011
What follows is intended as a general guide to airbrushes, and how to use them.
Types of Airbrushes
All airbrushes use a stream of pressurized gas (usually air, though CO2 may also be used) to atomize and spray paint in a more or less controlled manner. There are two ways in which airbrushes mix the air and the paint: externally and internally.
With an external-mix airbrush, the paint supply is pulled by siphon from a resevoir into a stream of air and dispersed via air pressure. This could be a simple spray-gun design or a more sophisticated setup with an open venturi nozzle. These designs are extremely rugged and well suited for broad application. Fine detail work will be very difficult. Careful thinning is required to avoid a spatter pattern. Only single-action airbrushes occupy this category. Examples include the Paashe H and Badger 350.
With an internal mix airbrush, paint is drawn via siphon or gravity feed into a chamber (nozzle) within the airbrush where it is mixed with air before exiting. Control is achieved by varying the paint flow. These designs produce a finer paint spray, but most are designed for relatively fine work (not spray-gun). These may be single or double-action designs. Examples include the Iwata Eclipse and Revolution; Badger 150, 200, 155; etc.
Controlling the Paint Flow
Air and paint flow are controlled in one of two ways: through single action and double action.
The trigger in a single-action airbrush controls only the air flow. Paint flow is controlled separately, typically via a screw mechanism on the nozzle. Single-action airbrushes may be internal or external mix designs. The primary advantage of a single-action airbrush is the ability to paint the same size line consistently. Once the paint flow and air pressure are set, the airbrush should continue to apply the same amount of paint through a project. A disadvantage is the opposite, it is difficult to taper or shade work with a single-action brush, the paint flow must be frequently changed to achieve this effect.
The trigger on a double-action airbrush controls both airflow and paint flow. This allows changes to paint application while working. Additionally, a double-action airbrush avoids a “burst-spatter” of paint built up on the nozzle when air is applied. Typically the trigger is pushed down to begin airflow and back to begin paint flow. A needle within the nozzle is controlled by the trigger via a clamp. Advantages include a broad range of paint application rate without making adjustments to the hardware, allowing a tapering effect. Disadvantages include hand fatigue from maintaining a constant pressure, a higher degree of dexterity compared with a single-action airbrush and the possibility of applying too much paint by accident.
There are two ways to deliver paint to the airbrush: by siphon or by gravity.
In the Siphon-fed type of airbrush, paint is drawn from a reservoir below the airbrush. The higher velocity of the airflow draws the liquid via reduced pressure, as Venturi showed. The biggest advantages of this type of airbrush are the ability to use a large bottle for paint and the possibility of changing paint bottles quickly during a project. The disadvantages include the requirement to use high enough airflow to move paint, with a linked disadvantage when trying to paint fine detail, and more equipment to clean.
On a Gravity-fed airbrush, a color cup is integral to the airbrush or attached via a side-port. Gravity draws paint directly to the paint-mix chamber. Advantages include using dilute paint and low air pressure because gravity helps the paint flow; a very secure paint chamber (if the cup is built into the brush it won't fall off); and the ability to use less paint per project. Disadvantages include a fixed cup size, more complex cleaning, and a potentially heavier airbrush.
Choosing an airbrush
Mastering your airbrush will be easier if you choose the correct one first. Will you have trouble holding a heavy brush? Do your hands cramp easily when held in the same position for extended periods? Do you have relatively poor dexterity? Do you require an airbrush which can apply very fine lines of paint? How large are your hands? Will you paint broad, mostly monochrome projects?
It's important to feel an airbrush in your hands and get an idea how it will work for you. Barring that, you should ask questions of people who you trust to give you good advice and can ask the right questions. A retailer can help you by letting you test an airbrush, but often retailers have a very limited selection. Still, your local shop will support the airbrushes they sell so you will usually have a ready supply of spare parts.
Becoming extremely familiar with one model of airbrush can make it difficult to switch to another. For example, if you're used to an external-mix airbrush you might find it a steep learning curve when trying a double-action detail airbrush. You might eventually find you need the capabilities of a detail brush, but you will have to practice a lot and “unlearn” a lot of habits which served you well in the past.
Airbrush cost is part of your decision. As with any tool, there is a broad range of costs and capabilities. The higher precision and higher complexity require higher costs. The fine detail airbrushes are very expensive but might be necessary for you once you've reached the limit of your current airbrush's capabilities. On the other hand, you might keep a very simple external-mix airbrush for applying metallic paints over broad surfaces. That way you don't risk contaminating other finishes with metallic flakes.
Replacing parts can become expensive. Some of the parts will routinely wear out, like a water pump on a car, the tips/nozzles and needles will wear out over time. Careful use and cleaning can minimize this, but eventually you'll need to replace that nozzle. The nozzle (tip) on an Omni costs $4 while on an Iwata HP detail brush it costs $35. The Omni is designed for general purpose use and the HP designed for precision use and you pay accordingly. This means you won't use the detail brush for painting large surfaces without a very good reason.
Like any other tool, if you take care of it, it will take care of you. Keep your tools clean and store them well and they will last a long time. Quality materials also make a big difference. Like most other things in life, quality does cost but the most costly may not be worth the money to you. The mid-range and higher cost airbrushes will feature stainless steel parts, or at least nickel-plated brass. Plating can be damaged over time, steel will not. Synthetic rubber and teflon seals need to be inspected and perhaps replaced over time. Rubber O-rings will leak as they wear, causing pressure drops and leaks.
Your nozzle and needle are the most vulnerable parts of your airbrush. The nozzle is one part of a valve, the needle is the other. These parts must mesh together well, but this creates the possibility of damage, particularly to the nozzle. If the nozzle opening becomes deformed you will notice a spattering or grainy paint pattern. If the needle becomes deformed or bent you will notice an off-center spray pattern and you could notice paint flowing when the trigger is not pulled back. A deformed needle will also damage the nozzle.
If possible, always remove the needle from the front of the airbrush, to minimize the chance of depositing paint or thinner inside the airbrush body. On some airbrushes this is not possible - the needle may have a ball on the end. On others it's inconvenient because the nozzle screws into its mount. In that case you need to be very careful and clean the needle as best you can while in the airbrush or unscrew the nozzle. Be very careful doing this, as you can easily drop or damage it.
You don't necessarily need to dissemble an airbrush after every use. Generally if I know I'll need to use it again very soon, and have done a good job cleaning the parts in situ, I'll leave it as-is. Otherwise, I break the airbrush down and clean thoroughly. This will involve an appropriate thinner, brushes, scrubber pad and plenty of water (in the case of acrylic paints). I use a small strip of 3M's Scotch Brite to scrub excess paint from the color cup, then run airbrush cleaner, alcohol or Windex through the airbrush. After, I'll remove the nozzle and needle, and clean them. The needle is simple enough, a quick wipe with thinner will do. The nozzle you should clean very carefully with a bit of rolled-up paper towel and thinner. If these seem very dirty you can let them soak in thinner for a while, but be careful with rubber seals as ammonia in Windex may damage them. Beyond these precautions, a brush and paper towel should be used to generally clean the airbrush.
There are a few airbrush cleaning kits available with handy brushes and other supplies. The very thin brushes are handy but can damage other metal parts so be very careful. Use them only if you suspect there is some gunk stuck inside. You may find your airbrush becomes very dirty at some point and you need to completely dissemble and clean every part. At this point, it's a very good idea to have your schematic on-hand. These are available online at the manufacturer's website.
Lubrication is important to allow the needle to slide easily in the airbrush. A couple of dedicated airbrush lubricants are available. A very small amount is sufficient. Apply by merely touching the dispenser to the needle and using what it picks up. Slide the needle through the airbrush only far enough to lubricate the chucking guide and spring housing. Avoid getting lubricant anywhere it will contact paint.
Thinning the Paint
Moving liquid through the airbrush is what painting is all about. It's a balancing act between being thick enough to cover well and thin enough to move without very high air pressure. Generally speaking, the air pressure used for airbrushing will be 12-15 PSI. For detail painting you will want lower pressure, so you will use dilute paint or even inks. The paint should become a fine aerosol and deposit smoothly on the model. Thick paint will leave a rough texture. Too thin paint at too high air pressure will tend to pool and "spider" on the surface.
In my experience, gloss paints are more tricky than matte. I typically add a little Tamiya or Gunze Flat Base to a gloss paint to make it semi-gloss. I find it performs more predictably and covers better.
Another very important step is masking your model. There are a few choices in tape; I prefer Tamiya tape - it's pliable thin, adheres well and yet releases well. Other brands are similar, but avoid regular inexpensive masking tape. The blue 3M low-tack tape is another good option. Don't rely on the egde of the tape to be perfectly straight right off the roll - if you need a straight edge, it's best to make it yourself with a fresh hobby blade and a steel ruller. For irregular paint patterns there are a lot of possibilities like Blu-Tak, Silly Putty, kneaded eraser, Play-Doh, Post-it notes etc.
It's good idea to seal a layer of paint with a clear coat before masking. This both protects the paint and gives a better surface for tape. Future (Johnson's Pledge with Future) or other acrylic coats are ideal for this. They cure quickly and provide a durable coat. Masking is tedious, you need to make sure the tape is secure and burnished into grooves etc. before you apply paint.
This page copyright © 2011 Starship Modeler. First posted on 23 February 2011.