When I write patterns for hand knitting I usually try to make sure that the decreases are worked on the knit side (right side) of the fabric i.e. even numbers of rows between decreases. However sometimes it is necessary to work shaping decreases every row for several rows which means having to decrease on the purl side as well as the knit side of the fabric. When you look at the purl side of a piece of stocking stitch which includes decreases, the decreases are not very visible but on the knit side the direction of the decrease is very visible. As a result it is necessary to work the decreases on the purl side of the fabric that will lean in the same direction as the knit decrease below or above it.
There are generally not as many variations of purl decreases in common use as there are knit decreases and in this post I am looking at the 3 most common methods of working single decreases on the purl side of the fabric.
Purl 2 together (p2tog) - right leaning decrease on the knit side
This is probably the easiest purl decrease to work as you purl 2 stitches together. When viewed from the knit side of the fabric this decrease gives a right sloping decrease so it matches the knit 2 together (k2tog).
Purl 2 together through the back loop (p2togtbl) - left leaning decrease on the knit side
This decrease is a bit more fiddly to complete. I find when I am working p2togtbl the first thing I do is to loosen the two stitches that are to be worked together by putting my right needle through the 2 stitches as if to work a p2tog.
Once I take the right needle out of these 2 stitches again I try to 'pinch' the knitting to keep the loops as open as possible so that I can then get into the same 2 stitches but this time trough the back loops.
Once the right needles in place through the back loops the 2 stitches can be purled together.
This decrease will give a left leaning slant on the knit side of the fabric so is often used to match the slip 1, knit 1, pass slipped stitch over (skpo) decrease. The stitches are knitted through the back loop which results in them being twisted at the base of the stitch.
Slip slip purl (ssp) - left leaning decrease on the knit side
This purl decrease is used much more frequently in America as it is the purl decrease to match the ssk decrease on the knit side.
Slip the next stitch knitwise to the right needle.
Slip the 2nd stitch knitwise to the right needle.
Slip both slipped stitches back to the left needle.
Purl the 2 together through the back loop.
Although this decrease is very similar to the p2togtbl and needs a couple of extra steps it does give a better finish on the knit side of the fabric as the stitches are not twisted.
The finished sample above shows how the 3 methods of decreasing look on the knit side of the fabric. Working from right to left across the sample, it starts with the ssp (left leaning) decrease, in the middle is the p2togtbl (left leaning) decrease and finishes with the p2tog (right leaning) decrease. As you can see the ssp decrease gives a much smoother line than the p2togtbl decrease.