Sunday, December 7, 2008

Provisional cast on--knitting up vs. knitting down

Back in December '06, TECHknitting featured provisional crocheted cast on. That post promised a future trick to get around a long-standing problem--that there is ALWAYS going to be one fewer loop working down than working up. In October '07, this blog showed another method of provisional cast on: the COWYAK method. In the comments to that post, a reader touched on the same issue, writing...

"When I unzip my provisional cast-on, why are there one fewer stitches going "down" than going "up," AND, what can I do about it?"
Look at your hand. If you are like most people, you have five fingers. But how many spaces do you have between your fingers? For 5 fingers, there are only 4 spaces between your fingers.

The same thing happens in knitting when you work the other way from a provisional cast-on. If you cast on a certain number of stitches and work "up," when you "unzip" the provisional casting on, you'll have one fewer live stitches to knit "down."

In other words, if you provisionally cast on 10 stitches and then undo the cast on, there will only be nine stitches waiting for you to pick up to knit "down." It's not a mystery--it's just the same thing as your fingers--ten stitches knitted "up" leave only nine spaces between them, and that's what you're picking up with the provisional cast-on--the nine spaces.

Of course, the "spaces" analogy is not perfect--we obviously have loops on the needle, not spaces when we catch the live loops from a provisional cast on. However, like the spaces between our fingers, these loops are the bars between the stitches, they are the stitch TAILS, not the actual loops themselves.

Below is a view of what this would look like in real life if you removed the provisional cast-on, took the needles out, and could make the fabric lie flat. See that complicated business on the right and the loop on the left? That's what happens when you pull out the provisional casting-on: The half loops of the rightmost and leftmost tails get pulled upwards to the next row, leaving only the full loops of the tails between the upwards loops: 5 upward loops make 4 downward tails, 9 upward loops make 8 downward tails. In other words, the pattern remains the same: always one fewer downward loops than upward loops.

Now, the upside (har!) is that there are at least two elegant ways to solve this problem. Actually, there is a very good third method which involves an alternative to provisional casting on, and a link will be placed here when that post goes live. For now, however, the two techniques...

TECHnique #1:
Let's say that you want to knit on 8 stitches. Try this trick: provisionally cast on 9 stitches. On the first and second row, knit all 9 stitches. On the third row, knit 2 stitches together (k2tog) where you think they'll be least obvious. In plain stockinette, see if you like the k2tog right in the middle, or if you find an edge less obvious. I vote for the middle of the row, but you must make up your own mind. On the illustration below, the needles and the provisional cast off have been removed, and the fabric has magically been made to lie flat. As you can see, the k2tog is in the middle of the row, picked out for you in green. There were originally 9 stitches cast on and worked "up," leaving 8 tails. However, after the k2tog, there are a matching set of 8 live loops at the top and bottom of this work.

To summarize this technique:
  • Provisionally cast on one extra stitch
  • Row 1 and 2: Knit every stitch going "up"
  • Row 3: Somewhere along the third row, wherever you think it will be least obvious, k2tog to get rid of the extra stitch going "up."
  • Rows 4 and following: knit normally
  • when the time comes to "unzip" the provisional casting on, you will have the correct number of stitches to knit "down."
TECHnique #2:
If the trick of REMOVING an extra stitch going "up" doesn't grab you, here's another alternative which has you ADD an extra stitch going "down."

Provisionally cast on the correct number of stitches, and work all the stitches "up" normally. Unzip the provisional casting on, catch the live loops on your needle, and on the second or third row knitting "DOWN," add a stitch by the "invisible increase" method (click here for instructions).

To summarize this technique:
  • Provisionally cast on the correct number of stitches
  • Knit every stitch going "up"
  • When you come to unzip the provisional casting on, you will find one fewer loops going "down."
  • Pick up the stitches going "down" and knit for two rows.
  • On the third row, add a stitch by making a nearly invisible increase.
Provisional cast on makes a 1/2 stitch discontinuity--a jog-- between where the stitches go "up" and where they go "down."

Not only is there always one fewer stitch going "down" than "up," but the offset between the tails and loops causes another problem, also. Specifically, when we knit "down" on the tail loops, the downward knitting is 1/2 stitch off the upward knitting.

Through an act of heavenly mercy, it turns out that stockinette is so symmetrical that this 1/2 stitch difference is very nearly undetectable in stocking stitch. To prove this is so, take any piece of stockinette fabric, look at it closely, then turn it upside down and look again. You will see that stockinette looks the same upside down and right side up. The only way you'll see the offset in stockinette is at the edge of the fabric, where the 1/2 stitch jog shows as a tiny bump on each side.

Other knit fabrics are not so forgiving. A continuous ribbed fabric would show a 1/2 stitch discontinuity between where the stitches are knit "up" and where the stitches are knit "down." To minimize this, provisional cast on is usually used along a border where the fabric pattern is going to change anyway: the classic location is at the border between the bottom band and the body of a sweater, or at the border between cuff and sleeve. Because the bottom band or cuff is likely to be made in ribbing, while the garment body or sleeve is likely to be made in a different pattern, the discontinuity -- the jog -- of the provisional pick-up line is disguised.

A quick aside: Do you wonder why you'd want to put the cuff on a sleeve via a provisional cast on? There are at least two good reasons to do it: 1. It makes it easy to replace the cuff, important for children's clothing. 2. It makes it easy to adjust the cuff length after the main garment has been knitted and can be tried on. You might want to put the bottom band on a sweater via the provisional cast on method for the same reason: picking up the bottom band and knitting it last would make it easy to adjust the final sweater length after the sweater body has been knit and can be tried on.

If you were making a garment with just one fabric pattern -- a pattern which would look bad with a jog -- you would have to arrange matters so that at the line of the provisional cast on, there would be several rows of plain stockinette stitch.

A common example is lacy scarf worked in a directional lace pattern. Specifically, in order to have the two lace patterns match at the lower ends of the scarf, you might want to start the scarf in the middle with a provisional cast on, and work first towards one end, and then towards the other. However, you might not want the 1/2 stitch jog to interfere with the continuity of your lace pattern. A classic solution is to design the scarf with a stockinette panel, as shown below.

Because the provisional cast on is in the middle of a stockinette fabric, there will be hardly any visible discontinuity where the provisional cast on lies--there will be a 1/2 stitch jog at the edges, but none in the middle of the fabric. Also, the shape of a scarf with a narrow stockinette pattern lies very well on the neck--the narrow bit goes around the back, adding no bulk behind the neck, while the pretty lace panels show in all their glory on the front. The best part about a scarf like this is that the narrow stockinette band has the same number of stitches as the lace panels--no increasing is required. The secret is that lace (pretty nearly any lace) is much wider than a stockinette fabric on the same number of stitches, due to all the yarn overs.

There is a scarf like this somewhere here at Chez TECH, but one of the little TECHlings has it hidden away. When found, a photograph of it will be added to this post...

(Some time later) Oh here it is!
You have been reading TECHknitting on: "Provisional cast on --one extra stitch going up, one less stitch going down; 1/2 stitch off in pattern"