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! 
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BTW, here is what a dump looks like when a 3.5" disk's metal hub is re-attached, but off center:
One would think that the cookie and the hub would be sized to match exactly, but that is not always the case.
And then there's those Wabash disks. Someone handed me a set of 5.25 they wanted me to archive for a fee, and I turned it back. I told them, they can't pay me enough to deal with those disks.
There was already shedding in the jackets.
@SomeGuy, what software are you using to get that image?
It's the HxC disk software (note you don't have to have the HxC hardware to use it)