Just as a single-stitch decrease starts out with two stitches and ends up with one, a double decrease starts out with three stitches and ends up with one. I was trying to think of examples of when you might see these, such as lace patterns, garment shaping, etc, but really, they can be used just about anywhere in anything you knit. The first one, the Central Double Decrease (CDD) is used quite often in lace patterns to bring a set of stitches to a peak. In such a case it is usually preceded and followed by a yarn over, so that the pattern for that area might read, 'yo, cdd, yo' Also, if the pattern is trying to create a flow of stitches that work towards the center of a motif, this increase would not be covered on either side with a yo, and would result in a ridge or design line in the fabric. I also like to use this when working mitred or modular pieces, such as in the squares of my Stained Glass Bag design.
To work a CDD, slip two stitches together knitwise (remember my rule about slipping stitches when they are part of a decrease) and knit the third stitch.
With the tip of your left needle, grab the two slipped sts on your right needle, lift them up and over the knitted stitch, and drop them off of the needle.
The result is a decrease where the central stitch lies on top, as you can see just above and to the right of my thumb. Look just below my thumb, and see what happens when you stack these on top of each other for several rows.
Sometimes you want your double decreases to lean in one direction or the other. This is pretty simple, and the right leaning double decrease and the left leaning double decrease are worked almost exactly the same, except for the order in which you pass the slipped stitches over. They both start with a slip one, knit one. To make the stitch lean towards the right, you next pick up that slipped stitch, and bring it up and over the knit stitch and drop it off of the needle.
Now take the knit stitch, put it over onto the left needle, and take the next unworked left stitch and pass it up and over the knitted stitch, and drop it off.
To have a double decrease that leans towards the left, start the same way, Sl1, K1. But you will immediately put the knitted stitch over to the left needle, and pass the next unworked stitch on the left needle up and over the knitted stitch.
Put the knit stitch with its slipped stitch collar over to the right needle, and bring that first slipped stitch up and over the knitted stitch, dropping it off of the needle.
Here you can see the right leaning decrease as the rightmost of the two shown, and the left-leaning double decrease as the leftmost of the two double decreases shown.
Just a heads up for you all, but tantalizingly without any details yet! The beginning of July will be the one year anniversary for this blog! Lynn and I have some fun and surprises planned around this, and I'll be revealing them to you sometime before the end of June. Trust me, you will NOT want to miss this. I had the germ of an idea, but it is Lynn who has put all the trimmings on the turkey, as it were. Keep your eyes glued here...