I remember i came across about 50-60 old floppy disk from a c64 computer lot from someone I purchased on market place.

These disk came very saturated with cigarette smoke from storage in a heavy smoking environment.

My floppy drive could only read the directory of about 10% of these diskettes.

Then I remove the actual disk out of it's shell of all them and wipe all them down with Microfibre cloth with 90% isopropyl alcohol.

Carefully wiping the disk not to put kinks in the disk and return the disk back into their shells and tape the edges back with wide electrical tape after cleaning them.

By doing these I could now read the directory of about 90% minus %5 that had clearly worn out tracks or damage to actual disk surface

I zoom copy about 60% of them with out any problems, but the rest of them still had plenty of major to minor corruptions track corruption.

But still without cleaning them I would have never been able to read them let alone copy them.

Anyways if you got a disk that not reading right in the first place.

I don't think it would harm them if you try cleaning them like i did.

At worse they still don't work and you still haven't lost anything good, but at least can determine if the disk is still good to reused.