The thing goes on. I'm trying to keep it simple so you can get it easily.
It's time for creating some "volume". No really hard tricks here, just new tones of gray. FLAT GRAYS.
Two layers. Linework below, tones above (multiply).
FAQ: How do i calculate light and volume?Art means Freedom. So let's not be attached to Laws of Physics (not this this time) So, If it LOOKS right, it IS right.
Some standard flat brush with... duh. White and black.
I change the transparency of the brush (very very often) to get a whole new range of tones.
FOR TEACHING PURPOSES, THIS WILL BE HIGH-RES AND DOWNLOADABLE.