SSK or Slip, slip, knit is a rather modern invention as a decrease.
SSK or Slip, slip, knit is a rather modern invention as a decrease. Two stitches are slipped to the right hand needle one at a time as if to knit, then the left needle is put through those two slipped stitches now on the right needle and they are knitted together. It is a left leaning decrease. Since K2tog (knit two together) leans right, the SSP and K2tog are mirror images of each other and form an attractive looking pair.
Older patterns wil use SKP (Slip one, knit one, and pass slipped stitch over the knit stitch) which does lean left but is not the mirror image of the K2tog. It does get the job done but I almost always automatically substitute SSK for the older K2tog.
How you slip the two stitches does matter. The first stitch is always slipped "as if to knit" and most instructions tell you to slip the second stich in the same manner, "as if to knit". Most times this works quite well. Keep in mind that as you slip each stitch, you are twisting that stitch a bit. When you knit those two stitches together, the left leg of the top stitch is resting on the twisted left leg of that second slipped stitch. In some yarns, this can cause a slight rise in the left leg of that decrease and show as a slightly raised stitch off the surface.
The prevention is simply to slip the second stitch straight across or "as if to purl". That keeps the second stitch flat as it prevents the elevation of that left leg of the top stitch. It is always safest to do a small sample to see if it matters how you slip that second stitch.
Slipping each "as if to knit" is a bit faster. When in doubt, I will do a small sample of each technique to see if it matters for the yarn I am using. Thus avoiding any ugly surprises!
A final note. As fuzzy yarns hide the stitches, either decrease works. Increases and decreases in lace are most often used for decorative purposes. Maybe the designer intended the particular look of the old SKP so do exercise some caution in substituting the SSK in lace.
