One of the most popular requests I get these days hobby wise is airbrushing advice. Here's an attempt to compile my thoughts and experiences thus far. This is more appropriate for those who learn better by doing things hands-on like me. A lot of this has been trial and error as I haven't sat down with any videos or classes since college 13 years ago.
I'll start with my airbrushing station as preparation and tools are very important.
Here's my station in my hobby corner. Well ventilated with several open windows and fans. The paint can on the left has several magnets stuck to it which I use to hold models since I put washers on the bases also. Water with a dropper/turkey baster in the middle. The compressor on the right is new and pretty nice and quiet. Paper towels for cleaning the airbrush. The foam core in the back is for catching over spray and test firing my paint and pressure.
Mastering your pressure and paint/water mix is key to not ruining your models. I currently paint at about 18psi and water my paints down to "heavy cream" since I use cheap acrylics not meant for airbrushing. Too much water or pressure will make the paint "spider" as seen above (bad). Proper pressure and dilution will allow you to paint in broad strokes or fine lines (good).
Washing out your airbrush is also key. I can usually paint for about 5 minutes straight before flushing the brush with water. I disassemble the unit and fully clean it between colors.
My main use for airbrushing is to provide a dynamic base coat to paint over with a brush. It's important to not attempt too much with an airbrush (IMO). Let me also say that my techniques are focused on saving time and money first. These aren't techniques that will win you painting awards, but they'll get new units and armies on the table quickly. I'll start with the new tyranid scheme which has very little airbrushing and will be an easier place to start.
Here's 3 bonesword warriors and an alpha warrior primed white.
First, I airbrushed Grass Green (FolkArt) on the base and tip of the swords and on their finger. These models are fully assembled as I was painting over my old green/black scheme. When airbrushing assembled models, it's important to hold them so you are spraying the needed part only and not onto the rest of the model. Sometimes you can do this by changing how you hold the model, sometimes you need a paper towel for a mask.
All swords and fingers finished with Apple Orchard. About 10 minutes in at this point for 2 colors and cleaning.
Next I even out the armor plates with Wicker White over the primer.
Then Ivory White down the center of the armor plates leaving only the outer edges. At this point my old compressor died so I went out to Harbor Freight and got the new (better) compressor pictured above. In the meantime, I applied a Violet Purple wash to the flesh over the primer.
I also applied an Apple Orchard wash to the guns. The washes for this phase are applied by brush and are VERY watered down. I want the washes to flow off the high points and settle into the details.
Back to airbrushing with my new compressor, I applied Tapioca down the center of the armor plates leaving more of the edge exposed than the last layer. At this level of precision, I test fire the airbrush on the paint can and on my hand before applying paint to the models. This way you minimize the potential for mistakes.
As a final airbrush coat, I use Honeycomb down the middle of the armor plates. This is pretty much a narrow line, leaving more exposed from all previous layers. This is where I switch over to washes and detailing. The airbrushing is just a basecoat to detail over. About 3 hours in at this point for the whole batch between airbrushing and washes.
Here you can see where I picked one model (front center) to finish as a test model.
Additional washes of Thunder Blue were applied over the purple skin to settle in the details. A black wash was finally applied to the joints, gills, and creases. Grass Green was washed over the Apple Green gun. Armor plates were detailed with Pure Black, Dark Brown, and Honeycomb from a very wet palette. The paint applied is more of a stain to the undercoat and more resembles a wash than a "layer" of paint.
Here's the carnifex using the same process.
A small 1,000pt force in progress. This represents about 2 weeks worth of free time if I get 2 hours a day. Not a ton of airbrushing, but it can be limiting if you're painting fully assembled models and want to use different colors.
Part 2 of this series will focus on blending base coats and focus on the dark eldar which have much more airbrushing. Part 3 will be directional lighting with the grey knights and maybe a sneak peek of my current project. Part 4 will be airbrushing bases.