When binding-off x stitches, you create (x-1) loops across the edge (because the first 2 stitches bound-off only create 1 loop). I propose that for a nice, stretchy bind-off, create more loops!
In this post, I will use the following abbreviations:
- YPCM: Yarn used per extra stitch bound off, in centimetres
- YPS: Yarn used per extra stitch bound off, in terms of bound-off stitches
YPCM is the length of yarn required to bind-off an extra stitch.
YPS is different from the others, because it is a measurement that controls for gauge. 1 YPS basically means 1 wrap around a needle. If you knit a stitch, that is one 1 YPS, and the same if you purl.
Therefore, the traditional Long-tail Bind-off has a YPS of 1, because to bind-off one more stitch, you knit the stitch, and then pass the previous one over. You only 'add yarn' once.
To give you an idea what YPS looks like for other Bind-offs:
- Long-tail bind-off: 1
- 3-stitch I-cord bind-off: 3
- JSSBO: 2.5 (0.5 extra because of reverse and purl yarnovers eat a bit more yarn)
- K2togtbl bind-off: 2
- 1 by 1 tubular bind off with grafting: 4
A sideways lace edging is super stretchy, but difficult to obtain a YPS measurement. It creates a longer outer edge than the inner edge that is being bound off, which gives the inner edge more room to grow.
(These numbers are not calculated by measuring yarn used, but instead by counting the stitches made to bind off an extra stitch.)
When you use a stretchy bind-off, you are using a technique that has a higher YPS, which consequently leads to a higher YPCM.
When you increase the needle size, you increase the YPCM but not the YPS. It will usually be faster than switching to a stretchier bind-off, because you will not need to make more stitches.
Create More Loops!
If you increase the number of loops in the bind-off edge to more than (x-1), you will increase the YPS and YPCM.
With the K2togtbl bind-off, this can be done by knitting an extra loop (or stitch, depending on how you see it) into the stitch on the right needle at regular intervals. Theoretically, to achieve the same YPS as the JSSBO, you will create this extra stitch every second stitch you bind-off.
I have actually never done that. I usually find that a loop increase of about 10-20%, or an extra 1-2 loops every 10 stitches, is sufficient -- this means a YPS of about 2.1-2.2. On my current mitten WIP, that seems to be enough so that I just slide my mittens on as opposed to feeling the tight edge as I tug it over the widest part of my hand.
Create More Smaller Loops for Cuffs!
By choosing the correct needle size, you could have a Long-tail bind-off that has the same YPCM as a JSSBO. It does not mean that the former is equivalent to the latter, especially in terms of good finishing. How you add the extra yarn does matter, and in my opinion, that is why some people (myself included), have trouble getting JSSBO to look good.
There are 2 kinds of stretchy edges that we commonly need in knitting.
The first is what we need for blocking things like lace, where we want to open the edge up. We want to have the ability to stretch, open up, and stay that way.
The second is what we need for things like cuffs and hems. We want it to have give, but to shrink back once we pull it over the right body part.
For the latter, I like to suggest that you need a relatively high YPS while carefully managing the resulting YPCM so that you do not have a flaring edge.
We can do that increasing the extra loops, to have a YPS of 2.3-2.4, and decreasing the needle size.
I will be back with photos at some point. I need to get a lightbox as I have trouble getting the close-up shots required.