Because 78s are too big for most scanners when you attempt to scan them the labels don't lie directly on the glass of the scanner. This often makes the scans out of focus.

If your scanner is relatively flat then I've found that placing a heavy book or a pile of magazines gently presses the centre of the disc onto the glass and creates much better results.

Not to be advised on your rare ones of course!

Just tried this on a rare one and it gave a good result

All my 78s are rare... okay, most of them!

Its the removing it off the scanner and catching the edge on the laptop cracking the disc thats the problem