When you knit a sweater, usually (but not always) you knit each piece separately: the back, the front (or each side of the front, if it's a cardigan), and both sleeves. Then you "block" the pieces, forming them into the shapes they'll take permanently, before sewing the pieces together and adding a collar/neckband/button band.
|Blocking the pieces of a sweater I'm knitting for my husband.|
With an animal fiber like wool, there's a lot of spring in the yarn (I'll skip the full technical explanation). This means that the sweater pieces can roll or smush together before blocking. Sorry for getting technical there. Blocking "teaches" the pieces how to lay right so they'll fit together better when sewing.
When you wash a wool sweater, you need to do the same thing. Let's say, for example, that you have curly hair. You can "teach" your hair to lay flat with a flat iron, but the next time your hair gets wet, it will "forget." You have to straighten it all over again, or it'll just spring right back up into its natural state. (Which is beautiful, by the way. Stop straightening it.)
So you can follow the same process you would for blocking a sweater to wash it. Note that it will take longer to dry because a put-together sweater is twice as thick as the individual pieces, so it would be better to use a lay-flat drying rack made of mesh to help with air circulation.
To block (or wash) a wool sweater--or insert "sweater pieces" whenever I say that--first you have to wet the sweater. Use cold water--hot water can cause shrinkage or felting--and a gentle cleaner like Woolite. I like to fill my washing machine to low, add the detergent, then stop the machine and stick the sweater pieces in the drum. (DON'T let them agitate--that's the other step to felting wool, and you'll ruin your sweater.) You can let them soak up the water on their own, or you can speed this along by squeezing them under the water.
Once the sweater is soaking wet, take it out of the water and lightly squeeze (DON'T wring) excess water out. (Why put so much in if you're just going to take some out? You want to get the fibers uniformly wet.) Be very gentle during this part--wet wool is fragile. For extremely delicate pieces, I use a clean kitchen colander to lift them so I don't put any strain on the fibers.
You can also squeeze out the excess water by placing the sweater on a towel and rolling the towel up with the sweater on the inside. The fibers are protected here, so you can squeeze or even stand on the towel to get that water out.
Once the pieces are damp, you shape them. You want features like cables and ribbing to stretch out a bit, while flat sections may have a tendency to curl. When you're blocking, you'll want to pin the pieces into that shape for the drying process, but that may not be necessary when you're just washing them. If you're using pins, use rust proof pins. Most knitters prefer stainless steel T-pins.
|Obviously not a sweater. This cashmere shawl I knit used a LOT of pins for every little detail. |
Lace needs "aggressive" blocking to bring out the details. Don't pull your sweaters this far!
For blocking, I usually use a towel over cardboard or my carpet (though I'm hoping to get one of those alphabet foam floor puzzles to use--they're fantastic!). I've also used a mattress for something I knew would dry very quickly.
Since you can stretch the sweater into the right shape here, you can also stretch it to fit you better here. If it's too short, you can lengthen it. If it's too narrow or tight, you can stretch it. You can do this to certain parts or the whole thing. But again, wool is delicate, so don't stretch it too much. (You could also try hanging a wet sweater upside down to lengthen it, but I wouldn't, because I think it would stretch the fibers unevenly.) If you're adjusting the size, you might want to use pins on a solid surface to hold it in shape.
I discovered a new trick when I was blocking my husband's sweater: I took a sweater that already fits him and used it to determine the best size for the pieces. (I was blocking them several inches too big before that!) Since patterns include finished sizes (and if you're lucky, piece sizes), you can also use a ruler to make it the right size. As you can see in the top photo, I also tried to line up the sleeves with the armscyes so they'd sew in better.
The pieces dry in that shape, and then you're ready to wear (or sew together) your sweater!
There are other ways to block wool, of course, but if you want to wash it, you'll probably want to stick to something that gets it all the way wet, right?
Note: blocking works best on natural fibers, especially animal fibers. It still helps with acrylic fibers, but the results usually aren't quite as dramatic, and resizing isn't recommended.