I finished it!
I'm very, very pleased with how this turned out. It's much better than I was expecting and really improves the room. Since I like it so much, I've decided to share how I made it. I've titled this post 'pattern' but it isn't really, it's more of a tutorial. I hope it makes sense, let me know if it doesn't. Please note I've used British crochet terms throughout, and this throw was designed for a single bed. If you want one for a double bed, you'll need to make more squares and arrange them differently. Obviously.
What I used:
About two and a half (I think) balls of Robin Aran With Wool, in an off-white
One ball of Cygnet DK, light blue
One ball of Cygnet DK, dark blue
A 4mm crochet hook
What I did:
The throw uses forty crochet squares, each 15cm/6 inches square. Mine were all chosen from 200 Crochet Blocks by Jan Eaton but you could use any that take your fancy. Crochet Pattern Central is a good place to start. They could be all different, or you could find two you like and alternate them, or whatever you want really. I made all mine in the off-white.
Once you have your squares, join twelve of them into a block of two squares by six. I joined the blocks by holding two together, wrong sides facing, and double-crocheting them together. I joined them all with light blue, then double-crocheted all the way round the edge, again in the light blue, to make it look neat.
After that I started what I call the granny-ing. I call it that because it's the same as the way you make a traditional granny square. If you've never made a granny square, it might be a good idea to practise a couple before you try the throw. Or you could jump straight in, making it up as you go along is how I made this throw after all!
Essentially, you want to treble crochet three times into the double-crochet foundation row, then chain two, skipping two double-crochets. Like so:
Continue round the edge of your central block in that fashion. Make sure that the chain-gap falls on each corner, and chain three instead of two at that point. You might need to fudge it a little to get the chain to fall in the right place.
I'm coming across as a terribly professional designer, aren't I? Excellent.
On the next go round, treble three times into each chain gap, and chain two across the top of the previous row's trebles, as you can see in the previous picture. At the corners, treble three, chain three, treble three into the corner space.
Then you'll need to check your gauge (I know, sorry). If your squares are six inches square, you'll need to do six inches of granny-ing before you attach the second lot of squares. I found that four rows of off-white granny-ing, then three rows of blue (light/dark/light), then four more rows of off-white, was pretty much spot-on six inches. Always worth checking, though.
After all that, time for more squares. Join them in a rectangle shape, so that you have ten down each of the long sides, and six down each of the short sides. Then join that to the centre of the throw that you've already made. That sounds easy-peasy, but it took me a couple of evenings, and when I realised I'd joined the second set of squares on upside-down I said some bad words and decided it could stay as it is. And that is why the square-joining looks different on each set of squares on my throw; because I'm a) unobservant and b) lazy. If the squares you've made have a definite right side then this may be more important to you than it was to me.
One other thing to be careful of is that you join the squares reasonably evenly. Make sure the edges of the squares matches from one set to the next, so that the throw will lie flat. Also if you have somewhere where you can lay it all out flat, that helps.
After joining on your squares, double-crochet round the edge again to neaten it, then time for more granny-ing! I did the same amount of granny-ing as before, so that is would match, and because me and my graph paper had worked out that that would make it the right size. Hoorah!
Only one more step! The edging. The granny-ing alone didn't make it look 'finished' so I made up a quick edging. Simply put, I went round one more time, doing treble three/chain two/treble three into each chain gap, followed by a single crochet into the top of the middle treble in the group on the previous row. Like so:
And then you are finished! And can make up the spare bed, and cover it over, so that the cat may sleep where he pleases.