Corrugated, or two-color ribbing, is a common decorative edging on many colorwork designs, including my Woodland Mittens. It has a great effect, but it can be a bit trickier than regular colorwork, which is usually done all in knit stitches.
I'm typically a "picker" or continental style knitter, but this tutorial will use both the "picking" and "throwing" techniques for the most efficient way to work this pattern. Not familiar with continental style? This is a helpful tutorial.
By working the rib with two hands this way, you don't have to fuss with dropping and picking up a different color for each stitch.
For the purposes of this tutorial, the green will be our contrasting color, or CC; and the grey will be the main color, or MC. This tutorial also assumes you will be working in the round.
One important thing to know before you start, two-color ribbing will have less recovery/elasticity than regular ribbing, so you may wish to go down a needle size, especially if you're replacing a solid rib with a corrugated one.
To start, cast on in your CC and join in round. Knit one round in CC.
Join your MC at the start of the round. From here, you will knit in the CC, and purl in the CC.
Take your CC, or the color you will be doing knit stitches with, and hold it in your right hand. Take the MC, or the color you will be doing purl stitches with, and hold it in your left hand, tensioning the yarn around your pinky finger as in Continental style. To begin, both yarns should be behind the needles, with the CC in front of the MC.
Step 1: With the yarn held in your right hand, work a knit stitch by "throwing" or wrapping the yarn around the needle with your right hand.
Step 2: Shift the left hand needle, so the MC yarn is in front of the work. Purl the next stitch Continental-style. Shift yarn back behind work.
Repeat Steps 1 and 2 until you reach the desired length of rib!