If I'm correct, in the second huntorial he's mixing latex and acrylics with water. That is not a great idear. You'll get into problems with your latex after a while.
A long time ago I found a tutorial on youtube to paint latex masks and I'm still painting the same way they showed on the video.
Here's what I do:
First get an airbrushgun with an external mix, I'll tell you later why.
Mix the acrylpaint with a small amount of latex, make it thinner with ammonia. You'll have to find out the thickness of your mixture, this depends on the diameter of your gun nozzle (hope I spell this correct).
You will see that the mixture is lighter, when it's dry you'll see that it is darker. Almost like the acrylic paint his original colour
This paint will not crack on your skin or mask, the latex keeps it flexible. But when you use an internal mix you'll see that after a few minutes you have to clean your gun because the latex in the paint will block up your internal mixing system.
For light shading you can use only acrylics with ammonia. Like that you can work in close details. This small amount of paint will not crack and the ammonia in your paint "chews" into the latex surface. Use the same mixture for drybrushing.
Always work in a ventilated area and wear some breathing protection.
When your finished, clean your airbrush gun, the ammonia is agressive against the copper layer in your spray gun.
