/ic/ - Artwork/Critique

I have two questions.

How do you keep your erasers sharp and without the pencil gunk? I tried eroding one with a nail file and the resulting texture was really unpleasant.

And the other - I'm doing this thing where I scan an unfinished pic, print it, and then finish off the copy because I'm too much of a pussy to do it to the original and I can maintain a "save state" this way. Let's say I draw a character in nude so I can draw clothes on them afterwards - my question is, how do I best print the nude character so I can still delete the printed lines and edit the clothes in?