edit: after talking with Ashley some more, I’m beginning to suspect that I’m just crazy and that I was actually right all along, even though I’m having trouble wrapping my brain around it. This will teach me to a) write about swatches seven months after I actually knit the swatch and b) try to apply brain power to anything not work-related the week before a deadline. So pretty much just ignore this post (I’m leaving it published for a variety of reasons), while I go knit some socks or something and watch Sons of Anarchy.
In response to yesterday’s post, Ashley asked:
So, what am missing? I thought the whole point of blocking your swatch was that you wanted to use the post-blocking gauge, since that’s how the garment will look/feel/act after it’s washed. Now I’m confused!
Yes, you do want to know how the garment is going to look and feel after it’s washed, you’re absolutely right. And so it is important to block your swatch in the same manner that you will block the finished piece. But if you use your post-blocking gauge numbers to determine the number of stitches you’ll be using when you cast-on, you’re going to get results that are different than what you intend.
Say you cast on 20 stitches for your swatch, and your pre-block gauge is 12 sts to 4″, and your post-block gauge is 14 stitches to 4″. That’s not a huge difference, 2 stitches to over 4″ (or half a stitch an inch), but if you then take the 14 stitches number to determine your cast-on numbers, it can make a big difference. If you’re going for a 40″ bust circumference, and you use the 14 sts gauge, you would cast on 140 stitches (14 ÷ 4″ = 3.5 stitches to the inch x 40″ circumference = 140 stitches for a 40″ circumference). You knit this imaginary garment, you finish it, you try it on, and it fits perfectly. But when it’s washed and blocked, it’s still going to grow. Probably by about 2 stitches to 4″ again. So your garment that fits the way you want it before you wash it is going to come out a little bit bigger after you wash it. If you wanted your garment to fit a 40″ chest, and you knit it with your post-blocking numbers, it’s going to come out too big (possibly somewhere in the 6–8″ range too big).
Prime example of this is my Vivian. When I finished knitting it, the sleeves were the perfect length. After I washed it, they were 6″ too long and I had to cuff them. If I had swatched with my yarn, and then washed that, I would have known before knitting them that my yarn would grow tremendously in the washing, and I would have made the sleeves shorter by omitting an entire cable repeat (and those Vivian cable repeats are big; that’s how long these sleeves are).
Specifically with my sweaterdress, since my stitch count decreased (12 stitches pre-blocking to 11.5 stitches post-blocking), this could potentially lead to negative ease, which is not what I want. However, when I tried on the yoke, it’s coming out a bit bigger than I wanted, so I think some puffing up of the stitches (and therefore the slight half a stitch decrease over 2″) will work in my favor.
The part where my gauge differences is being problematic is in the row gauge. My pre-blocking row gauge was 17.5 rows to 2″; post-blocking, it was 19 rows to 2″. I did the math for my decreases based on the post-blocking gauge, which means they were initially spaced out a little too much (and this is the subject of another post).
So, does this help?
Hmm…I’m still not sure.
Let’s take the numbers from your example:
12 sts/4″ before blocking implies that 1 pre-blocking stitch is 1/3″ (~0.33″) long
14 sts/4″ after blocking implies that 1 post-blocking stitch is 2/7″ (~0.28″) long
(So in this case, the fabric actually shrinks during blocking–more stitches per inch means each stitch is shorter. They have to be smaller/shorter, so you can cram more into the same length.)
If I c/o 120 sts (as indicated by the pre-blocking gauge) to get a 40″ bust, it will fit perfectly at first, but will shrink during the wash to a circumference of 120 sts * 2/7 inches/st = 34.3 inches (approx).
If I c/o 140 sts (as indicated by the post-blocking gauge), the garment will be 46.7″ around at first, and then shrink down to the 40″ bust after the first wash. Which is what we want, right?
***
For your dress, where you have fewer stitches per inch after blocking (11.5 instead of 12) your fabric is actually growing, so that will give positive ease, yes? (Positive ease is looser, as I understand it.)
I’ll have to go back and re-read your earlier posts about the details of the design to figure out what I think about your row gauge issue. But that is for another time, and a night with more brain power!
that actually makes sense (specially since, depending on yarn, I’d guess) you would have either growth or shrinkage? So you’d have to know both before and after blocking. Right?
You are not crazy! It’s just tricksy hobbit math!