With more and more superwash yarns popping up, it's becoming harder to avoid them. Many hand dyed yarns are superwash and if you've fallen in love with a beautifully dyed, one of a kind yarn, sometimes you just need to knit with it.
When wool yarn is treated to become "superwash" it is stripped of it's natural elasticity properties. It won't spring back into shape after being soaked in water. It grows in size. And this can ruin a carefully hand knit garment.
But there is a way around this. You can knit with a superwash yarn and have your sweater turn out as expected. You just need a bit of planning and math. (just a little).
I always list in the notes section of my patterns that are worked in superwash yarns, to measure lengths vertically with the weight of the garment hanging from the needles. But there is just so much explanation that you can write into a pattern before it becomes tedious to read, especially for knitters who are already know this. So I'm taking a few moments to elaborate here, and arming you with the knowledge and steps to take to be able to knit a garment that fits with superwash yarns.
1. Knit a swatch. As a wise knitter told me once, "We all knit swatches after all! We either knit 4x4" swatches or 18x20" swatches." With superwash yarns, this is a must!
2. Measure the UNBLOCKED swatch. Write down your stitch and row gauge over at least 4".
3. Block it. Soak it in water, roll it in a towel, lay it flat, pin it and let it dry.
4. Unpin it and fluff it out. Lay it back down and with a ruler, measure the dry, blocked swatch and again write down your stitch and row gauge over 4".
5. Your stitch gauge, after blocking, must equal the stitch gauge of the pattern. Some patterns list both the pre and post blocking gauges, and if they don't, it is standard practice that patterns will list the gauge after blocking. If your stitch gauge doesn't match, try a different needle size, make a new swatch, and measure it before and after blocking.
6. Once you have a blocked swatch that matches the pattern's stitch gauge, use this swatch and figure the percentage that your swatch lengthened. Compare your pre-blocked row gauge to the post-blocked row gauge. If the pre-blocked row gauge is 32 rows=4" (8 rows=1") and after blocking it's 28 rows=4" (7 rows=1"), 8 div by 7=1.14. The length increased by 14%. You can also measure the new swatch. If the old one was 4" and the new one is 4.57" 4.57/4=1.14.
If the swatch is 10% larger, then it increased 110% of the original size. This equates to (110/100) or 1.1. This is the number you'll need.
10% = 1.1
15% = 1.15
20% = 1.2
22% = 1.22 etc.
(If blocked is 10% larger, you can't just reverse it all and say the pre-blocked swatch is 90% smaller. It's close, but not accurate.)
7. Back to row gauge! If your blocked swatch was 10% larger, you'll divide by 1.1 remember. Use this knowledge when knitting lengths. When a sweater says to "work until piece measures 18" and divide for armholes", you'll want to lift your needles up and measure the length with the weight of the piece hanging from your needles. Place the tape measure just under the needle so you're measuring the last row of stitches worked that are lined up under the ones that are on the needle. Let the tape measure hang until it reaches the bottom. You'll stop knitting when you've reached the length called for in the pattern, in this case 18" divided by 1.1 which equals 16.36". That is a big difference, especially if you're working sleeves.
Since you've done the pre/post block experiment, you know that, in this scenario, a piece of knitted fabric measuring 16.36" unblocked, will grow 10% after blocking and become 18". The percentage changes with every project. Yarn, needle size, tension, and stitch pattern all affect the percentage of growth. So you'll want to do this every time you're knitting with superwash yarns.
If you're unsure of your math, or just nervous about proceeding, you can always stop 3-4" short of the length that the pattern states to knit to, take a tapestry needle threaded with yarn and run it through all the stitches, remove your needles and soak the unfinished piece. Block it and measure it after it's dry. This will help you to figure out how much more you need to knit before proceeding. Once it's dry just re-feed your needle into the stitches, remove the waste yarn and continue on. You can always start knitting the sleeves or front while it's drying, because we need to keep knitting right?
There are many reasons why you might end up knitting with a superwash yarn, and I hope this helps you to knit garments with confidence. You've mastered the hardest part - knitting stitches into a lovely fabric. By tweaking your process just a tad, you'll end up with a garment that fits. And expand your repertoire of yarns in the process.
If you have any questions, please email me at email@example.com.