The back join (one more time)The back join is usually used in circular knitting (around and around) because back-and forth knitters usually change at the fabric edge. Therefore, the illustrations below show the back join in circular knitting. You can, however, do the back join in flat (back and forth) knitting--see number (8), below.
So, suppose you are knitting around and around on circular needles in LAVENDER and you want to switch to PURPLE. One vital piece of information you'll need to figure out is EXACTLY where you want the color change to be. The first two steps in the illustrated instructions below are MEASURING steps. As you get better at the back-join, you can skip steps 1 and 2, but for the first few times, it probably makes sense to go through all the steps.1) (above) Begin the back join by knitting to the last LAVENDER stitch. Now you need to somehow locate and mark the spot on the tail, just PAST this last lavender stitch. This is the spot where you will interlock your lavender and purple yarns in step 3. You can mark this spot with a pin or a paperclip, or you can mark the spot by pinching it--the illustration shows the spot being marked with a pinch.
2) (above) Once you have this spot marked, UNRAVEL the last three stitches you have knit, and RETURN the unraveled stitches to the LEFT NEEDLE. If you are pinching the yarn to make the spot, you have to keep hold of the spot as you unravel. If you are marking the spot with a pin or clip, you do not have to keep hold of the spot as you unravel--the pin or the clip remains in the tail to mark the spot. The illustration above shows the three last stitches already unraveled, and returned to the left needle. The knitter in this illustration chose to mark with a pinch, and therefore is keeping hold of the spot to mark it.
3) (above) In step 3, you will INTERLOCK the old color (LAVENDER) with the new color (PURPLE) at the spot you have previously marked. You do this by folding the PURPLE yarn over the LAVENDER yarn at that spot. The LAVENDER yarn is now folded back on itself, creating a doubled strand--one strand is the yarn coming from the work, the other is the strand going to the ball. The PURPLE yarn is also folded back on itself, and again, a doubled strand is created, with one strand of yarn coming from the ball of purple yarn, and the other strand being the tail--which you should leave plenty long--several inches, at least.
4) (above) Anchoring the LAVENDER end of the interlocked strand up against the fabric with your right hand, and anchoring the PURPLE end of the interlocked strand over your tensioning finger, re-knit the next three stitches. Because the LAVENDER portion ends at the very spot you have marked, and because this spot is just past the last of the three re-knit lavender stitches, your color change should wind up exactly where it ought to be. (If the color change ISN'T where it ought to be, just unravel, and move the interlock.) The illustration above shows a continental-style knitter with the interlocked doubled strands of yarn wrapped over the left forefinger, but an English-style knitter would do everything the same, only just wrap the interlocked doubled strands of yarn over the right forefinger.
5) (above) After re-knitting the 3 LAVENDER stitches, the interlocked yarn automatically will be at the doubled PURPLE strand, and you will knit the next three stitches with both strands of the purple. After three stitches, drop the purple tail, and continue to knit normally with a single strand of purple yarn. When you get to a good stopping spot, separate the lavender yarn from your work by snipping it free, leaving an excess tail of a few inches on the back of the work. The illustration above shows the result after the six stitches of interlocked yarn have been knit, the tails themselves are worked in, and the excess of both tails have been left on the back of the fabric. Because the tails have been doubled BACK on themselves, this join is called the BACK JOIN.
IMPORTANT NOTE: When you get to the color change spot on the next spot, do not be confused by all the doubled stitches--knit only 1 stitch into each doubled-strand stitch in the round below--you should get 6 stitches in this area, not 12. This is the same situation as when tails are anchored with an overlapping join in single-color knitting.
6) As stated above, the more you use the back join, the better you'll get at it. Pretty soon, you'll be able to completely skip the measuring steps of knitting, marking and unraveling (steps one and two) because you'll have gained a pretty good idea of just where the interlock should occur. In other words, as you gain experience, you'll be able to start the process from step three -- you'll be able to interlock in the correct spot without having to stop and measure first.
7) After you have made up and blocked the garment, you do not need to work the excess tails in any further--the actual tails are already worked into all those doubled stitches. Simply snip the excess of the tails about 1/4 or 1/2 inch from the back face of the fabric and leave them there. If the garment is woolen, then after another couple of washings, any excess tails which haven't matted themselves onto the back fabric face may be clipped off short. If the garment is made of cotton, acrylic or any other "slippery" yarn, you are probably better off just leaving a short length hang on the fabric back for all time--less chance of having the excess of a tail pop through to the fabric face as you move and stretch.
8) If you want to do the back-join in flat knitting (back and forth on two needles), or if you want get fancy and reduce the bulk of this join, or if you want to combine this join with the "jogless join" technique, there is information about how to do all three of these things at the original back-join post.
I apologize to those of you I confused the first time. Hopefully this version of the instructions will be easier to follow.
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PS: Here is a link to a post with 10 (!) different methods of working in ends in knitting, eight of which are "as you go."
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(You have been reading TECHknitting on "back to the back-join.")