Why do good floppy disks go bad?

[Jon Elson]

On 04/06/2016 10:20 AM, Swift Griggs wrote:
>> 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?
Gap?  There IS no gap on a standard floppy.  The head 
contacts the media surface.
(Bernoulli drives did have a gap, and spun at a much higher 
RPM.)

But, on most single-sided floppies, there was a felt pad 
that pressed the media against the head.
The only gap might be when the head load solenoid is 
de-energized, the pad retracts and the media pulls away from 
the surface.  That was used on the old drives with AC motors 
that spun the disk all the time.

Most double-sided drives pinched the media between the two 
heads, and the DC motor shut off when there was no 
reading/writing for a while.
>
> 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.
>
>
All floppies and magnetic tapes have some kind of binder to 
hold the oxide to the backing, and it does deteriorate over 
time.  Ozone and other air pollution probably makes it go 
bad faster.

Jon