October 2016 Flyer Page 4 Basics of Airbrushing

4 Even after years of experience, youre going to encounter problems when airbrushing. Heres a peek at some of the problems Ive run into. Overspray. Watch where youre aiming your airbrush. While youre concentrating on spraying a certain spot, parts of the model that lie behind your target may accidentally receive overspray as you paint. Make sure you mask these areas before airbrushing. If you forget, you may have to repaint the affected areas. Gritty finish. The paint is covering, but its rough or lumpy. There are four possible causes: the paint isnt thinned enough, the airbrush is too far away and the paint is drying on the way to the model, clumps of pigment arent dissolving in the thinner, or theres too much air pressure. You dont need to blast on paint with an airbrush - a gentle whisper from the airbrush should be enough to deliver a smooth inish. Adjust the air pressure and make sure the paint is well mixed. Spatters. Little spatters around fine lines are usually caused by a damaged needle or nozzle. Paint deflects off the distorted tip and lands outside of the intended area. Sometimes, low air pressure can also cause this. Examine the needle and nozzle with a magnifying glass. If the nozzle is cracked or splayed open, replace it. If the tip of the needle is bent, you can carefully straighten it. Single-action needles are relatively sturdy, and you can persuade a bent tip by pressing it against a hard surface. Go easy: press, check, press some more, check again, and so forth. The fine needle of a double-action (or hybrid) airbrush is more delicate. You may not be able to see the bent tip, but youll be able to feel it. Remove the needle from the airbrush and drag it lightly over your fingertip. Roll the needle as you drag, and you'll feel the hooked side catch as it rubs along your finger. Make note of the direction of the hook, then drag the affected side of the needle on fine-grit sandpaper or a sanding stick. Check it again on your finger and repeat if necessary. Bleed under masking tape. This is usually caused by applying paint too heavily. The wet paint overwhelms the masking tape and creeps under, resulting in a ragged line. Spray on several light coats instead of trying to cover quickly with a heavy coat. Also, spray at an angle over the tape so the air pressure isnt forcing the paint under the mask. No paint coming out. Shame, shame. You havent been cleaning the airbrush properly. Most likely theres a small particle of dried paint clogging the nozzle. Read the sidebar Airbrush cleaning and be sure to clean your airbrush after every session. Paul Boyer, FineScale Modeler Airbrush troubleshooting are needed, but some, such as a pressure regulator, are useful. Small compressors are typically rated between 25 and 35 psi, ideal for most projects. However, for weathering you don't need that much pressure, and the regulator will let you adjust the psi. A moisture trap is another helpful feature. Humidity in a compressor can cause water droplets to pass through the airbrush and onto the model, ruining the paint job. If you're unable to find a compressor with a moisture trap, you can splice a trap directly into the air hose. Moisture traps should be drained after each painting session. About the only drawback to air compressors is that you can hear them running. Some compressors have an automatic shutoff feature to keep it from running when not in use. "Silent" models that use refrigerator-style compressors to charge small storage tanks are also available, but they're more expensive. Types of paint Once you have an airbrush and air source, the next thing you need is paint. The two types of paint used by model railroaders are acrylics and organic-solvent-based. Organic-solvent-based paints have been used in the hobby for many years but must be handled with care. These paints may attack plastic, so you'll want to prime your models or apply a protective coating. Also, organic- solvent-based paints must be used in a well-ventilated area, and you should wear a respirator, safety glasses, and nitrile rubber gloves. Safe for plastic, acrylic, or water- based, paints are available in the same range of colors as organic-solvent paints. Even though they're labeled as non-toxic, acrylics should still be used with caution (rubber gloves, respirator, and vented spray booth). Acrylics require a bit more air pressure (20-30 psi) than organic- solvent-based paints. Acrylics and solvent-based paints are both sold ready for brush painting, which means you need to thin them for airbrushing. Start by stirring the paint thoroughly in the jar. It takes several minutes to remix a bottle of paint, particularly if it's been sitting on the shelf for a while. Tans, grays, and browns take the longest time to mix because a large percentage of their pigment is clay. Keep stirring the paint until the pigment clumps are mixed completely with the liquid.

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