I have seen problems with floppies that were stored in my garage for a while. I think it may be a combination of moisture (I've got a vent from a bathroom in my basement that goes out there plus there's the water that evaporates from my car) and extreme cold in the winter.
Veterans may recall the temperature requirements on the sleeves of 5.25" floppies. A 3M DS/DD 5.25" floppy diskette sleeve states that a disk should be stored between 50 and 140 degrees Fahrenheit (10 and 60 degrees Celsius). I know for a fact that my garage can be less than 10 (or 50) degrees in the winter based on the readings of my car thermometer (which I have in Celsius; it has read as low as 6 degrees). I'd imagine the temperature requirements for 3.5" floppies would be the same since the material inside is identical.
I too was looking to format some 800K disks and found not one of the group of six I had pulled from my garage worked when I attempted to format them. Looking to see if it was a fluke I also tried a high density disk. That disk formatted yet it immediately had write errors. I then tried one of the failed 800K disks again and it formatted fine.
I should note that I formatted the working 800K disk in my SE, which runs System 6.0.7. The failures came in my LC, which runs System 7.1. I'm not sure if the system version had anything to do with it or not. The disk worked for what I needed it for (moving two MacWrite documents from one Mac to the other) without showing signs of error, yet I am not going to trust it as a longterm backup solution.
Try using System 6 to see if that makes a difference. I'll have to try it on one of the failed disks on the LC to see if it has something to do with my LC's floppy drive.
Veterans may recall the temperature requirements on the sleeves of 5.25" floppies. A 3M DS/DD 5.25" floppy diskette sleeve states that a disk should be stored between 50 and 140 degrees Fahrenheit (10 and 60 degrees Celsius). I know for a fact that my garage can be less than 10 (or 50) degrees in the winter based on the readings of my car thermometer (which I have in Celsius; it has read as low as 6 degrees). I'd imagine the temperature requirements for 3.5" floppies would be the same since the material inside is identical.
I too was looking to format some 800K disks and found not one of the group of six I had pulled from my garage worked when I attempted to format them. Looking to see if it was a fluke I also tried a high density disk. That disk formatted yet it immediately had write errors. I then tried one of the failed 800K disks again and it formatted fine.
I should note that I formatted the working 800K disk in my SE, which runs System 6.0.7. The failures came in my LC, which runs System 7.1. I'm not sure if the system version had anything to do with it or not. The disk worked for what I needed it for (moving two MacWrite documents from one Mac to the other) without showing signs of error, yet I am not going to trust it as a longterm backup solution.
Try using System 6 to see if that makes a difference. I'll have to try it on one of the failed disks on the LC to see if it has something to do with my LC's floppy drive.