Oh wow opsimath that is fascinating. I love darning and I wish I could find one of those things that looked like a gourd that was used to darn socks - my gran had one and the sock was pulled tightly across the ball of it to facilitate the darning.
So that's another job that no longer exists - making those things. I wonder what they were called?
My gran was the local town's most accomplished 'invisible mending' specialist. Sometimes she'd 'pinch' bits of fabric from inside seams etc to make repairs. I remember how proud I used to be of that when I was a child, that my gran could work her magic on a tear in an expensive dress or suit, and how happy it made her clients, I can still picture some of the dresses. So is 'invisible mending' still a job?
And maybe those memories are why I love darning ...! Just realised that. The only person in my family who brings stuff to me for darning is my son, he loves 'saving' his clothes. I'm not as good as my gran was though.