I’m not the best painter out there, but I’m reasonably experienced at painting minis with an airbrush. I wrote this up for the Facebook BT painting group, but I thought it might also be useful here.
Equipment:
1. Gravity-fed double-action airbrush with a small needle. Gravity-fed airbrushes can run on lower pressure, letting you get closer to the subject. They also hold less paint, but that's not important for small subjects. (Note: If you're only going to be priming and base-coating, siphon-fed is fine, and is recommended for large subjects like terrain so you're not constantly refilling.) The smaller the needle and the lower the air pressure, the finer the line you can paint. Double-action means the air on/off isn’t connected to the paint amount. This lets you run the air, then gently add paint until you’re putting just a little on. You can do almost transparent effects this way. (I use an Iwata Eclipse HP-CS.)
2. Compressor. Cans of air are expensive over time, and their varying pressure makes it hard to paint consistently. If you don't already have an air compressor in your garage (and don't plan on getting one for air tools) get an airbrush compressor -- they're much quieter and more portable. If you *do* want to use a big compressor, make sure it's oil-free (or have a *really* good oil trap). I know compressors cost as much as the airbrush itself, but look, you're getting an airbrush to save time painting -- don't cheap out now. (I use an Iwata Sprint Jet.)
3. Paint. Yes, you can thin out your regular paints. But unless they're good paints with fine pigments *and* you shake them a lot, you might get clumps. Clumps clog your airbrush, and you just lost 10 minutes stripping and cleaning. I use Vallejo Model Air. Again, why cheap out? The idea is to save time -- watering down craft paints and running them through a coffee filter works, but life is too short. (A note on acrylics vs enamels: I use exclusively acrylics so I can paint indoors. Don't aerosolize solvent-based paints without a mask, and either use a serious fume hood or go outside. Also, cleaning enamel out of an airbrush requires even more solvents.)
4. Fume hood (optional). Yes, I use acrylics, but I also don't want paint dust getting all over my workspace (which is also my home office) or my lungs. Something with a fan and a filter works nicely. Failing that, at least make sure you have a dust mask and a screen, unless you want your backsplash/wall (and lungs) to be slowly painted. (Search “hobby spray booth” on Amazon. Make sure it has a fan & filter.)
5. Airbrush stand (optional). If you lay a gravity-fed airbrush down on its side, the paint falls out. I like the little jars that hold the airbrush and traps spray so you can run cleaner through without just spraying it everywhere. (Search Amazon for “airbrush cleaning pot”.)
6. Practice (required). Get a sheet of paper and figure out the right pressure to paint. Try getting up close and painting fine lines. Experiment with how low you can get the pressure before the paint starts to splatter.
The painting process:
1. Miniature preparation. Airbrush paint goes on thinly. *VERY* thinly. Clean all the mold lines. If you leave file marks, get a different file and remove them, especially if you’re planning a light-colored paint job. When you’re done, put the mini down and move on. Come back the next day and look it over, preferably in different lighting. See that bit you missed? Fix it. Now, optionally, wash the mini with a toothbrush and soap. Rinse carefully. This will get all your finger oils off. Since you’ll be using an acrylic primer, this is more important than it is when using solvent-based spray primer. Now use a hot glue gun to glue the bottom of the mini to the lid of an empty water bottle (I use iced tea bottles due to the wider lids). You now have a handle, allowing you to move the mini around (don’t want to leave a ‘mech’s armpits unpainted!) without getting paint all over your hands and wiping paint from the base… or worse, dropping it!
2. Prime. I use Vallejo Model Air primer, usually in grey. Coat until you can’t see metal, usually one coat plus retouching. Allow to dry thoroughly. I know a guy who swears by a hair dryer at this step to speed drying so you can move on, but I tend to work in batches so that the first one is dry by the time #8 is primed.
3. Base coat. Go a shade lighter than you think – miniatures look darker than larger objects when painted the same shade. (Experienced mini painters can ignore that – you know what you’re doing.) If you’re doing camo, your base coat should be the lightest color of the camo pattern. I usually do a light green for forest, or a tan for desert.
4. Camo. (Optional.) Take one darker shade of a similar color and give your ‘mech stripes. Dark green for forest, brown for desert. Keep the stripes small; to do this, get closer. Don’t put the paint full-on; instead, have the air on and add just a little paint with the trigger (this is why I so strongly recommend a double-action airbrush). Repeat with a contrasting darker color – brown for forest, maybe a sage green, grey, or different hue of brown for desert. Use less this time. (You can also do fades here – not camo, but things like the WoB white fading to black at the extremities. *Much* faster than blending and drybrushing.)
5. Clear coat. No, you’re not done, but in addition to being thin, airbrush paint goes on very porous. This means any wash you do will soak in everywhere, not just in the dark spaces. Use gloss acrylic medium, or my favorite, Future floor finish (I forget what it’s sold as now – my bottle is still going strong). Just a light coat, enough to seal the paint.
6. Detail. This is where you go back to normal brushes. You can do panel lines, drybrushing, and washes to your heart’s content.
7. Clear coat. This is the protective coat. Heavy acrylic until it’s shiny everywhere when fully dry. Then maybe a little more.
8. Matte coat. Most brush-on matte varnishes (acrylic) will run through your airbrush just fine. Do a single coat; it should look like there’s not clear coat at all when you’re done. Matte does a poor job of protecting the paint, which is why the above step comes first. If your mini starts looking shiny after use, add more matte.
