Now I still have a day or two before I get back to work, I decided to try Karol-Ann's excellent suggestion of dyeing some donated curtain lining to make some kits up for jars quilts. DD recently dyed a charity shop dress black in my machine, and not only did the dress come out black, but my subsequent washing didn't!
Here is the cream-coloured lining fabric, waiting to go in the machine.
Here is the dry, dyed fabric. It is darker than it looks in this photo, a very dark charcoal, but not quite black. I suppose it was my fault as the instructions said the pack would dye 600 grammes of fabric, and I put in just a little more. Never mind. It'll be fine for jars quilts, and so long as I keep some back for borders etc. nobody will notice.
Especially when the jars are full of things like these which I picked up recently!
Local people, look out for the kits in my Project Linus box!