Right Leaning Decreases
In my experience the decrease that most people learn first is the Knit 2 together (k2tog) decrease. It is a fairly easy decrease to work but a lot of knitters are not really aware of how it makes the knitting look. When you work a k2tog decrease the second stitch lies on top of the first stitch and when viewed from the knit side of the fabric will lean towards the right. (When viewed from the purl side the directional lean of decreases is not that visible)
Decreases can be worked at the very edge of the knitting but generally I prefer to work decreases at least 1 or 2 stitches in from the edge as this gives the knitted fabric a smoother edge for sewing up or picking up stitches. Working the k2tog decrease 2 stitches in from the end of a row will give a column of 2 stitches leaning towards the right following the same direction of decrease as the actual edge The image below shows the left hand end of a piece of stocking stitch where the k2tog decrease has been worked 2 stitches in from the edge.
If you work the k2tog decrease at the beginning of a knit row i.e. knit 2, k2tog, the decrease will still lean to the right although the edge itself is decreasing towards the left. Working this decrease at the beginning of a row will give a less defined edge as can be seen in the image below.
However there are occasions when decreasing like this gives a better result e.g. when decreasing in a Fair Isle pattern one stitch from the edge, the second stitch sits on top of the first stitch and helps to keep the continuity of the pattern.
There are other ways of working a right leaning decrease but as they involve a lot of moving of stitches I have not found the need to work an alternative right leaning decrease.
Left Leaning Decreases
The k2tog decrease makes a very smooth right leaning decrease but the left leaning decrease generally used in the UK does not give as smooth a finish. The method used to work a left leaning decrease is, slip 1 (knitwise), knit 1, pass the slipped stitch over (skpo or sl1, k1, psso). In this decrease the first stitch sits on top of the second stitch and leans toward the left when viewed from the knit side of the fabric.
Because this decrease does not look as smooth as the k2tog decrease, knitters over the years have tried other methods of working a left leaning decrease that more nearly matches the k2tog decrease. Barbara G Walker came up with the slip slip knit (ssk) decrease which is generally used in American patterns. For those of you less familiar with this method of decrease you slip the next 2 stitches (knitwise) one at a time to the right needle. Put the point of the left needle through these 2 slipped stitches (from left to right) in front of the right needle and knit the 2 together.
You may ask ‘why not just work a knit 2 together through the back loop’. This will also give you a left leaning decrease and is often used in older Scottish patterns but by knitting through the back of the loop you twist the stitches. Working an ssk decrease the stitches are re-orientated on the needle so they are not twisted. The image below shows a sample where the ssk decrease has been worked 2 stitches in from the beginning of a knit row. This gives a column of 2 stitches leaning to the left, following the direction of decrease and giving a smooth line of stitches for picking up along the edge or seaming.
As with the right leaning decrease it can also be worked at the end of a row (still 2 stitches in from the edge) but this time the decrease is leaning in the opposite direction to the decreasing edge.
There is a variation on the ssk decrease that has been developed in recent years. In the original ssk decrease the next 2 stitches are slipped knitwise one at a time to the right needle. However if you slip the first stitch knitwise but the second stitch purlwise and then complete the decrease as before; the resulting left leaning decrease is flatter than the original ssk decrease.
In the sample below I have worked 3 methods of left leaning decrease, the right most decrease is skpo, followed by the original ssk and then the alternate version of ssk. In the picture they may not look that different but the left most decrease line gives the smoothest, flattest finish.
Once you understand the visual impact of different decreases you can choose to use the best decrease for the finished result you are trying to achieve. I will write another post about working decreases on the purl side of the fabric and also about using decreases when shaping garments.