If you are talking about AR-15/M-16 mags they do not need to be refinished.  They are (almost all) made of aluminum and the body will not rust.  You cannot blue them as blueing is a form of rust and it cannot be done on non-ferrous metals.  The crappy scuffed off finish is purely cosmetic and does not affect the function of the mag.  It does, however, give you an excuse to get them cheaper in many cases--"I don't know, looks pretty rough . . ." [}:D]  The floorplate and spring can rust but it is easily removed with steel wool, and replacing them is easy.  I have heard of spray painting mags, but that would likely make them too tight to fit in the mag well.  My advice, which is worth what you're paying for it, is to replace the black followers with green ones (in 30 rounders) and leave the cosmetic stuff alone.  Also, replace springs as needed, which is nearly never.  Good luck and welcome. [:)]