Hubby got some pretty socks out of Kureyon Sockyarn last year. They were a present for him when he moved in with me. I was pretty pleased with the way they turned out, Nice colorway, great fit. I knew the yarn is not as sturdy as Opal or Regia, so I took some black Regia for the heels and toes and I handwashed them.  It wasn't enough for these socks to be as durable as other socks.
I had darned them before, but the ball of the foot was totally worn out. What to do now?  Throw them away after sparsely a year of wear? And the legs and heel were fine, wouldn't it be a waste of work? 
I worked up new toes. 
Grandma, darner extraordinair, would be proud. 
