We all have seen various projects here and there about drawing with a simple 2 axis and 1 servo machine. I had no time to research about them mostly becouse i always try "myway" first but I'm quite sure you can take practically all the technologies and methods described in those projects and instead of using the servo to make a pencil go down, use it to push a single-action airbrush button.
To achieve this, the "brain" of the machine must be able to control both, servos and steppers. I Just know about Arduino Mega + Ramps + Marlin configuration, but I'm sure there are many other ways to get the same point.
Mounted on a 3 axis machine, the airbrush can be positioned closer or further away to achieve different results. You could make lines at different heights or make lines in wich height variates along their path.
I practically have no idea about airbrushing or other artistic drawing skills, but used some youtube tuts to learn the basics of airbrushing and tryed to "teach" my machine to reproduce it.
The hardware and gcode is ready for airbrushing, but i could not find the appropriate open software to generate the gcode. I can imagine that using 3d printing slicing software you can make quite a bunch of things, just editing the generated gcode a little to fit your idea.
So in the end, this group is mostly intended for sharing ideas and develope together things, methods and applications about this.
I hope you join and we all grow together!