onion skin

hey guys i was just wondering if any of you can answer my question, it would save me some time with expirimenting. when you are dealing with onion skin should you draw the skins that would be in the back first before the later skins? and is there any way you can go back and draw things to be under other skins?

hopefully that made sense :-\

Onion skinning refers to the fact that you can see through multiple drawings in a stack to view relative changes in your drawings. The term comes from the fact that really translucent paper use to be made from the skins of onions. So this technique is used to allow the animator to compare current drawings to previous or next drawings. In general, key pose drawings are made first to establish extreme positions of a movement. Then inbetween drawings are made. Most inbetweening is done utilizing onion skinning to view the key drawings while you work on the current drawing which is the in between. The number of inbetweens and how they differ from the previous key and the next key is a matter of the timing that the animator is using for the action. -JK

To learn more about keys and inbetweens here is some reference material to read:
A Good Place To Start