Preserving Floppy disks by reading raw flux data
Tech Tangents talks about how preservationists use tools like GreaseWeasle to back up disks.
It helped me a lot when learning how to back up and write my own disks.
Update: Using a Greaseweasle and a 5.25″ floppy drive turned out to be critical evidence/court records on a nearly 50-year-old floppy disk last written to in 1993 using a DEC PDP-11.