Whenever I work in public on a crochet project that I am going to felt, inevitably someone will ask me what I am making. When I answer, and add that I will felt it when I'm done crocheting, the next comment is, "I didn't know you could felt crochet." Well, yes you can. It may not felt just like a knitted piece does, but crochet does felt!
What you need to felt something is yarn that felts, hot water, and something that will provide agitation.
To felt something by machine – put the piece into a zippered pillowcase (this will prevent the felt lint from getting into the washing machine and gumming up the works). Use a small amount of hot water – you don't need much. Add something like an old towel, old jeans, or rubber flip flops. Something that the piece can bump around with. Add just a touch of laundry detergent, and start the machine. You might want to add some boiling water, too.
You should check your project every few minutes. Then, when it's felted enough, take it out. DON'T let it go through the rinse and spin cycles – this could put creases in the felted piece. If it doesn't felt enough in one wash cycle, drain the machine and start again. When the piece is felted enough, take it out, rinse it in cold water. Do not wring the water out of it (see above about rinse and spin cycles.) Roll it up in a towel to squeeze water out of it. Lay it flat to dry, and if it needs shaping, pull it into shape. If it needs stuffing, stuff the inside with a towel or some newspaper to wick the water away.
Now – how do you know how much your piece will shrink? You don't. :-)
You can make a swatch, measure it before and after felting, and get some idea. But it won't always be accurate. Small pieces felt differently than large ones do. Different yarns felt differently. Different colors of the SAME yarn felt differently. If the water is not as hot, if the agitation is not as strong or as long, your piece will felt differently. There are so many variables! And, crochet pieces felt differently than knit pieces. Crochet felts more in the width of the piece than in the height. Knit felts more in the height then in the width.
Look at the above example. Two bags, the red one is knit, the violet one crocheted. Both are worked in Berroco Vibe. Both were worked to the same initial size. Both were felted in the same machine, but not at the same time. See how the knit bag is not the same size as the crochet bag! It's shorter than the crochet bag, and the crochet bag is a little narrower than the knit one. If you look close, you can see the different width in the handles too.
I like to tell my students that felting is not an exact science. But it's fun to do, and you do get "hooked" on it!
