I received a book, and I cannot tell what caused the discoloration on the back page.  I'm posting a pic here for opinions, please.  Does this look like yellowing from age, or like a stain?  It is kind of a dark yellow in color, but it's not on any of the pages, just the back cover of the book

http://s225.photobucket.com/albums/dd318/bethany9529/PBS/?action=view&current=IMG_0359.jpg

Thanks everyone for your help!

Looks like a stain to me. Strange that it did not get onto the facing page.

Since there is no bleed out, and any kind of liquid would spread through paper like wildfire since it absorbs so much, I'd put it down to some kind of flaw in the paper itself.

Probalby sometime in the past the roll of paper that sheet came from was flawed or damaged in some way and that's the way it's aged. Books aren't made from one continuous roll of paper, but from several seperate printings put together. So one flawed piece of paper among good ones wouldn't surprise me.

So I'd just chalk it up to age.

I would say age -- I've seen some older paperbacks that have that on the covers and nowhere else.

thanks guys!  That was my thought too, since I didn't see damage anywhere else, even on the facing page.  Dont know if I will post this one back in the system, but I will mark it as received on my end!