Purling two stitches together through the back loop is not a common stitch used in knitting. Even some of the most experienced knitters have to look up this technique as it's quite rare due to it's difficulty.
While it's similar to P1 TBL (purl through back loop), it has a couple additional steps. If your pattern says "P2Tog TBL," limber up your wrists because it's time for some fancy needlework.
How to P2Tog TBL
"Purl 2 together through the back loop" (or P2Tog TBL) is a rather counterintuitive way to decrease stitches on the purl side. Yet, once you understand that it's going to feel awkward, it gets a little easier.
To make the stitch:
- Approach the two stitches you want to purl together from the back and from left to right (rather than from right to left). Read this with needles in hand and work the stitch (it doesn't make a lot of sense on paper). This is really the only way to have the needle in the right position to grab the working yarn in order to form the stitch.
- Cross your wrists behind the work and inserting your needle from the side opposite of what you normally do. Slip the point of the right needle in the back of the second and first loop, starting from left to right.
- Next, wrap your yarn string around the right needle in a standard pearl. Bring the yarn through the two loops and let them slide off the right needle. You've now completed the purl decrease stitch.
It's often been said about this tricky technique that if you feel like you're doing it wrong, you're likely doing it right. After a little practice, it's not that tricky and it's an interesting and useful way to decrease on the purl side.
You probably won't run into this stitch very often, but it's important to know for those few occasions when you do. You'll find it in patterns like the Cat's Paw and Striped Stocking that have a few twists, turns, or precise shaping.
More Advanced Knitting Decreases
This purl decrease will likely be one of your least used knitting stitches. More often, your pattern will call for one of the following:
- K2Tog (Knit Two Together): The most basic decrease, you will use this along with SSK very often to reduce the number of stitches on your needles.
- P2Tog (Purl Two Together): Just the opposite of the K2Tog, this stitch is most often done on the purl (or wrong) side of your work.
- K2Tog TBL (Knit Two Together Through Back Loop): If your pattern calls for P2Tog TBL, then it's very likely that you will need to know this one as well. It's just the opposite and worked on the knit (or right) side, but there's no knitter's gymnastics needed.
With any of these decreases, you might be asked to decrease three stitches rather than two. In that case, the stitch abbreviation will replace the number and everything else will stay the same (for instance, K3Tog and P3Tog).