I promised a pattern. I finally got the pictures I need taken, so here it goes.
The initial knitting makes a thing that looks like this:
I don't recall what stitch pattern I used, but it really doesn't matter. Keeping in mind that both sides of this will be visible, you can use just about any stitch pattern you wish. I'm fond of moss stitch, but I got bored with it when I made this (two or three years ago).
Use worsted weight yarn. Size 7 needles. The gauge is 16 sts and 29 rows over 4 inches, but the gauge isn't too critical. As long as you're in the ballpark, a stitch or two over or under this won't make that big a difference.
Cast on 54 sts.
Row 1: work evenly in your stitch pattern
Row 2: increase 1 stitch each at beginning and end of row. (56 sts)
Rows 3-7: work evenly
Row 8: work 18 sts, work one-row buttonhole over middle 20 sts, work to end (18 sts)
Rows 9-13: work evenly
Row 14: decrease 1 stitch each at beginning and end of row. (54 sts)
Row 15: bind off
Now comes the fun part. (And by fun, I mean that this sat for two or three years before I got around to it.) You'll need wire. I recommend 18 gauge wire for this. I've used 20 gauge and 16 gauge, but 18 gauge seems to be the sweet spot. Craft wire is fine. You'll need a piece about 40 inches long, although don't measure. You'll want to eyeball it.
You'll want it to look kind of like that. It should go around your piece, but with a lot of extra space. Then you need to twist the wire ends around each other to make a loop.
It should surround the knitted piece with about that much room. The knitting will stretch to fit.
The twist doesn't need to be that tight.
This will stay together because the wire is next fully encased in duct tape. (This is where I could use a better idea, so if you know of a better way to do this, please let me know).
I find it best to cut a length, then divide that down the middle and wrap it around. (Using the whole width of duct tape is a little too much.) I start with where the ends overlap, and then I encase the rest of the wire. (I have yet to do this and have the duct tape wrap the wire evenly.)
Then, grab a crochet hook that easily fits into the edge stitches (F or G), and using reverse single crochet (or crab stitch), crochet around the whole of the piece, making sure to crochet over the wire. (A regular single crochet would work as well. You could also just whip stitch the wire to the knit piece. I like the look of reverse single crochet, so I use it a lot.)
This bit is a bit fiddly. I suggest starting near the middle of one of the long sides. The last little bit is still hard, but it isn't as hard as if you started on one of the short ends.
You could use the same yarn that you made the piece out of, but I used white
because I can't find the yarn I used so that you could see the edging stitches. Someone also suggested that you could use a novelty yarn (like an eyelash yarn) for the edges giving the whole thing a bit more flair.
I have several of these (and now I have one more!), and I use them all the time. The wire does wear out after a while (a couple years of regular use), but it's easy enough to cut the old wire off and attach new when that happens.
The main trick is learning to get your hair put up in it. I had to practice for a while before I got the hang of it, and still I have to use a mirror.