I have seen this on some tapes that have been played - or rewound -  
on misiadjusted tape decks, so that they were wound at some time with  
the edges badly aligned. Some of them would go back to normal if  
properly played and stored, and some would not.

Whether they are mylar or acetate might be good information to have.  
I'll let the real experts step in, just wanted to say I have seen  
something like this too. I dont' know the real answer.

Lou Judson  Intuitive Audio

On Feb 9, 2009, at 4:15 PM, Frances, Melodie wrote:

> All,
> Forgive my newbie-ness but I am looking at a collection of reel-to- 
> reel
> audio tapes that we have and I have noticed that some of them have  
> what
> I would describe as kind of 'pre' cupping - that is, they aren't
> drastically curved and don't look like pictures of real cupping that I
> have seen, but they are a little bit curved, and when I look  
> through the
> clear plastic reel, the outer 1/8 - 1/4 of an inch looks different  
> from
> the rest of the tape - like it is not lying quite as flat.
> SO - how bad is this? Is there a word for this? I have looked  
> around on
> the web but mostly found stuff about true cupping.
> Thanks so much.
> Melodie Morgan Frances