I spend more time than is healthy on Old Sewing Machines - note the capital letters, as they are Important... And I belong to
Treadleona group of Old Sewing Machine Collectors and Users
And there has been a big conversation about all that thread that gets left on old bobbins, and wound on top of with the next colour, and how some people just can't bear to throw it away...
Personally, I unwind it all and junk it - the underneath layers are compressed to uselessness and the outer layers can have only a few feet - the record is 38 colours on one bobbin.
I made the postcards from Old Sewing Machine Fabric, unwound threads, and net. First two OSM users to ask, can have....