This is the first of an intermittent series about how to do little things in knitting that are hard to find. Double Decrease (sometimes DD or dec2), is used frequently in lace patterns to make a "point" at the tip of leaves or whatever is the center of the lace pattern. Often double decrease is given as the instruction "sl 1--k2tog--psso". And this is how that looks.
I was doing a practice swatch of a lace pattern, and there are these hideous double decreases up the middle of each "leaf." (The little white arrow is pointing to the ugliest one).
The problem is that the slipped stitch that is then passed over, always stretches. Even in single decreases, the same issue arises. Right-leaning single decreases, aka k2tog, are nice and flat (on the left in the blue knitting). Left-leaning single decreases, either ssk or "sl 1--k 1--psso", somehow always turn out lumpy (on the right in the blue knitting). This problem is only exacerbated in double decreases.
(Btw, I have heard that only regular knitters (ie people who don't knit "continental") have the problem of the SSK and PSSO loops getting stretchy, something having to do with the amount that each stitch is twisted. So this is for those of us who are not so lucky to be continental knitters.)
To make a better looking double decrease, first let's dissect out what exactly it is. We start with three stitches, that need to become one. We'll call the red one on the left L, the brown one in the center C, and the peach one on the right R. (Very tricky so far). The different methods of double decrease basically "stack up" the stitches in different order. Since there are three stitches, the six possible orders (from top to bottom) are: RLC, RCL, LCR, LRC, CRL, CLR.
The most obvious double decrease, is k3tog. This makes an LCR pattern, ie the L loop is on top, the C loop is in the middle, and the R loop is on the bottom. While easy, this decrease leans to the right, and will make asymmetric lace. Basically, the L is doing a k2tog (right-leaning decrease) over the C, and the C is doing another k2tog (right-leaning decrease) over the R, and so you end up with a very right-leaning double decrease.
So a good double decrease need to be balanced, ie be made up of one right-leaning decrease, and one left leaning decrease. Right leaning decreases include k2tog, and passing over a loop on the left needle. Left leaning decreases include ssk, and passing over a loop on the right needle (psso). Slipping two stitches simultaneous will swap the order of the stitches, and will make a rightward lean.
The other issue to address is how to get the correct stitch on top. In the brown lace swatch above, the R ends up being on top, and becomes the most prominent of the three stitches. (the picture is upside down) This, combined with it being stretched and ugly, makes the lace unattractive. The topmost stitch is the most visible, so if you want a symmetric lace, ideally the Center stitch will be on top. This leaves CRL and CLR as the two good options for lace.
Before the instructions, in case there is any confusion: by "sl" or "slip" I mean to slip knitwise (left pic). But "slide," I mean to move the stitch without twisting it, aka "slip purlwise" (right pic).
First, the CRL decreases:
Method 1: sl 2 (C and R) simultaneously. K1 (L). Pass C and R over new stitch.
This is balanced because slipping the two together produces a rightward lean, and the passing over on the right needle is a left-leaning decrease. The C loop is stretched because it was slipped and passed over. No pics as I don't like this decrease for this reason, and there are other pics of this method available online. This is the only CLR or CRL that doesn't use a cable needle, that I know of.
Sl 1 (R). Place next stitch (C) on cable needle, hold in front. sl 1 (L).
Insert left needle into front loops of L and R, and finish like an ssk.
Slide this new stitch on cable needle. Pass C on cable needle over new stitch. Slide stitch back on right needle.
This is balanced because there is an ssk (left-leaning), and a passing over a loop on the left (or cable needle in this case) (right-leaning). Again, the ssk portion stretches out the R loop, so although it is not on top (and not as visible), still the decrease is not quite perfect.
The CLR decreases:
Slide 1 (R) onto cable, hold in back. Sl 1 (C). Slide R from cable needle back onto left needle.
(first picture shows C being slipped)
K2tog (R and L together). PSSO.
This one is balanced because there is a K2tog (right-leaning), and a passing a loop on the right needle (left-leaning). The top (C) loop is the one that is passed over, so it is, again, stretched out and prominent, so it is not too great.
The recurrent problem is the asymmetry in the sizes of the loops., which is always caused by an slip or psso. K3tog produces the most uniform loops, but how to make it balanced? After much tinkering, here it is:
Method 2 (THE BEST double decrease EVER!)
Slide 1 (R) onto right needle. Slide 1 (C) onto cable needle, hold in front. Slide 1 (L) onto right needle.
Slide C from cable needle back onto left needle. Slide L, then R, back onto left needle as well.
K3tog. (Do this with just the thinner tip part of the right needle, NOT how I'm doing in the pic, to make it the prettier).
Hooray! This produces nice, uniform loops, as there are no ssk or psso's involved, and the C loop ends up on top. This is balanced by the k3tog (right-leaning), and by swapping the C and L loops (left-leaning). Using a cable needle to slide stitches, rather than slipping them, prevents too much stretch.
More on all the different double decrease combinations next time. And a re-swatch of the lace pattern too!