FEATHERING:
Feathering is a very very common technique used by inkers. It's probably eve more common than cross hatching, but it's a little more difficult to achieve than cross hatching.

This diagram shows the difference between the original pencils, bad feathering and good feathering. Sometimes, the penciller will indicate that he want feathering to go in a particular area, but he wont put very much detail into it (1). So if the inker comes along and inks it exactly the way the penciller has sketched it, it won't look very attractive (2). It up to the inker to make it look good (3). #2 is bad feathering, #3 is good feathering.

This is just another example of original pencils, bad feathering and good feathering. This one, however, uses long stroke and has more of a fade out effect than the previous one.