Just to apply my thoughts about copyrights to the original question of this thread:
"If I were to trace redraw or other wise reproduce an existing design, and add more or not , is that similar to a copyright violation ?"
It depends. There is a provision in the Copyright Law known as "Fair Use," which means there are lots of ways in which you can use another's work without violating the law. Items that are sold specifically as stencils or stamps are Fair Use, the designer's intent is clear, they want you to reproduce those images. Other areas of Fair Use are open for interpretation, such as commentary or satire.
There is another aspect of the law where the line is very clear ... you may not violate copyrights FOR COMMERCIAL PURPOSES. If you are a pottery student, and you are incorporating copyrighted materials into your work, or copying a famous potter's forms, and planning to give those pots to your mom, go for it! As soon as you start selling your pots for money, it better be free of these violations. It is against the law. And truthfully, as others have pointed out here, you could probably get away with it, but that doesn't mean you should.
BTW, everyone should understand that the link to the article about Shepard Fairey is an OPINION PIECE. It is not a legal analysis, and in my own opinion it is totally off base. It is basically the same argument as "it's ok to travel in the game of basketball, as long as you are star player, and your dunk was really awesome."
Right on Mea - Fairey is cutting it very fine on parody with the "Obey" work, and he probably has crossed the line into derivative work on many occasions. Any reasonable person can see it; it really doesn't matter how good the derivative is, because it's still the right of the original creator to create derivatives.
His real problem is that he doesn't want get permission to make the derivatives. And, he could. He really could. He'd have to share his profit, and that would be just too bad, wouldn't it?
As far as I can tell, creative people would be better off if they ignored the entire idea of fair use. It's not even a real doctrine - you either have a permission (license) or the expression is in the public domain. There's parody and commentary - but how often does that apply, really? Not often. There's some rights associated with owing the art itself, but it doesn't usually effect the core rights to copy, derive, or display. Educational use is still limited in all kinds of ways. And, I'd even suggest that you could still suffer statutory damages even if you never made a dime on a copyrighted or derivative work. So, yeah, better not make a tracing of someone else's work without their permission.