This sounds normal.  There needs to be margin in between your designs and the edge of the plate.  Otherwise, there will be light leaks from the side of the negatives which would affect the designs on the edge of your plate.  I would have to see your plate to be sure though.

Soak the metal in vinegar.  It’s smelly but works.  I’d mix 1 part vinegar to 1 part water (more concentrated works faster, but then you have to buy a lot more vinegar!).  The acid (acetic acid) will react with the rust and float to the surface of the liquid.  If you don’t have a container large enough for soaking, vinegar-dipped rags will work, although not as well. 

 

You can also rub a cut lemon on the metal (citric acid), but this will leave a slightly sticky film that you’ll need to wipe off later.  Good luck!

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