Archiving and cleaning 3.5" floppy disks
3.5" disks can be a pain. This latest set I have been working on archiving was a real mess. It was a dual 3.5"/5.25" set, the boxes had some mildew on them, and the 5.25" disks had a thin layer of gunk, on the surface. Fortunately, my usual 5.25" cleaning got the nasty crud off of the 5.25" disks and got a good read. But the 3.5" disks were much more challenging.
An initial inspection of the 3.5" disks looked like the surfaces were clean with only a tiny bit of touch up needed. But noooo, put one of the disks in and it started to scratch itself up like crazy. Just Q-tip cleaning did not seem to help. You can't just open the shutter and run water in to it, the water won't go where you want. So I just soaked and rinsed them them in hot water, accepting that might damage the labels.
The big pain, as always, was drying. Fortunately, it was a dry day and leaving them on a blower with the shutters taped open for most of the day got them dry enough. Followed up with some q-tips and isopropyl alcohol where I didn't see any scratches (avoid using isopropyl alcohol on scratches or shedding).
That seemed to help stabilize things, what invisible gunk remained on each track seemed to disappear after a few reads, rather than getting worse. Re-dumping the scratched disks managed to get a good enough read with only damage in unused space.
One little tip: Don't try to rotate the metal hub too hard if a 3.5" disk is wet or otherwise won't easily turn. They can come undone fairly easily.
Also, just for the heck of it, I experimented a bit using a hair dryer to dry a disk I didn't care about. It is well known those will warp the jackets on 5.25" disks. But although a 3.5" disks case is ridged, it can warp the cookie inside. (Gooey cookies! )