Why do good floppy disks go bad?

[Swift Griggs]

On Wed, 6 Apr 2016, JP Hindin wrote:
> - Repeated use slowly wears away the magnetic media layer on the mylar.

There is no doubt that there is some friction there.  However, I'd be
surprised if this was the chief cause.

> When left in an unprotected state, or a poor environment, damp, mold and
> dust can damage the surface, either degrading the magnetic layer or
> causing the gap to shrink enough that the drive head physically damages
> the disk?

I have serious doubts here.  While there is no question that contaminates
could ruin a disk, a drive, or both, I doubt it's the main cause.  Many
floppy disks are kept in pretty pristine conditions.  I know mine are, and I
still have bad sectors.

> - Quantum fluctuations in the state of the universe, caused by millions of

:-)

> Of course, after ten years, it could be your own memory that's failed.

That'd be my problem. That or being embarassed by what I find *uncorrupted*
on the floppies like college-age poetry and what-not. 

> Dare I ask, what's the consensus?

I'll go way off the rails and say that I beleive it's mostly due to
oxidization of the ferromagnetic particles on the floppy itself. I've also
heard smarter people than me claim that some floppies used "binders" for the
particles on the disk which are attractive to some forms of mold. 

-Swift