February 25, 2014

Controlling fine line intensity with an airbrush

I've tried to airbrush freehand fur before, which wasn't really successful. The reference image wasn't very good (printed on an old HP 1010 B&W laser printer) as a result of which I wasn't able to make good use of my lightbox. I am currently working on an other project for which I had the reference image printed in a print shop. The image that I found on Internet, was not high res, but good enough to see most detail. The beard texture in the recent project is not entirely similar to the fur texture of the panther's fur, but it requires a similar technique.

Failed attempt at properly airbrushing fur

I will try to explain it here. The aim is to spray around the white hairs and airbrush the shadows and darker hairs. This requires the airbrushing of fine lines of various intensity. As is explained in the Yogi airbrush portrait blog entry, I use an Iwata HP-BH airbrush with a polished needle, the air cap removed and Vallejo Premium waterborne acrylic paint. This paint works very well, but requires some attention. See the Yogi article for mix-ratio and air pressure. When fiddling with the trigger at some point the spray will be stable. But in airbrushing this is merely a temporary stability, because the paint inevitably builds up around the needle and nozzle tips.

The exact instant when the build up will result in no paint being pushed out of the airbrush, often followed by a sudden release of paint - the dreaded spider - is difficult to predict. As a rule of thumb, when paint has trouble flowing out of the gun, briefly blow the airbrush with the trigger all the way back and pressed down on a piece of paper that is not the art work. I always keep a piece of A4 paper in my left hand close to where I am airbrushing and use this to regularly check the stability of my spray and to 'reset' the airbrush by blowing paint residues and air 'full throttle' several times. This usually removes most of the clogged paint from the airbrush internals.

Inspired by the magnificent Alberto Ponno...

Also cleaning the airbrush is very important. Personally I spray water then thinner and then water again after each color change or when I stop airbrushing. Also - very important - turn air pressure down until air just comes out and pull back and press the trigger all the way - then tap the index finger of the hand not holding the airbrush against the tip. Turn up air pressure gradually and slowly when doing this, but not too high or you may end up with air bubbles in your circulation - which is NOT good. Water or thinner will now bubble in the paint cup. If you rapidly tap, it will send tiny shock waves through the fluid and particularly when there is thinner in the cup paint residues will be solved and pushed back in the paint cup. When you see shards of paint in the paint cup in the bubbling fluid, don't spray again but throw it away by turning the airbrush upside down above a cup or something else to catch the fluid. Make sure the shards of paint do not stick to the inside wall of the paint cup before spraying to clean again.

Now the prerequisites are mentioned, the fine spraying goes as follows: When a stable spray is found, it can be kept alive by very subtle, minimal movements of the index finger controlling the trigger from just before and just past the 'sweet spot'. It is almost more changing the tension in the finger in an alternating way than actually moving the trigger. Mind you, this is a method that merely postpones the instant at which the airbrush stops giving paint when spraying very fine lines, allowing the artist to spray fine lines for a longer period of time. When the slight movements of the index finger become necessary to persuade the airbrush to continue to give paint, it is a sign that sooner or later the airbush needs to be blown through to reset the gun.

Try it. It works.