Last Saturday, I went to a meeting of the Sheffield Knitting & Crochet Guild - I don't know why I hadn't thought to do that before, because Sheffield is not very far away, and it's my home town, so I enjoy visiting once in a while.
The Sheffield Guild meets once a month, and has a topic for each meeting. On Saturday there was a class on double knitting. In case you don't know, it's a technique for producing a double thickness of fabric, with the two layers linked together. You knit with two colours of yarn: each layer has a design in one colour on a background of the other colour - but the colours in one layer are the reverse of those in the other. I managed to produce a tiny sample during the meeting. It's not very well done - the tension is uneven, and the edges are untidy. (It would have looked a bit better if I had decided in advance that I wanted to do a design over an odd number of stitches, and cast on an odd number in the first place - then at least the design would have been in the middle.) But if I tried again, I'm sure I would produce something better.
It's a nice idea - you get a thick fabric that is equally presentable on both sides, plus the intriguing effect of a 'positive' and 'negative' two-colour design on the two sides. But it's slow - at least as slow as knitting the two sides separately, I think. So I don't have any plans to knit anything in double knitting, but I'm pleased that I now know how to do it. And I'll go to meetings of the Sheffield Guild again - it was a good afternoon.
Later, I found a tutorial on double knitting by Ann Kingstone. She describes a good way to get a neat edge in double knitting - my sample would definitely have benefited from it.