Double Knitting

Note - I've used two colors to enhance visibility. This is NOT how to do two color double knitting. The mess of ends you see is a result of the two colors, you won't have all of those tails doing one color.

Side A

From Double Knitting

Side B (note the odd green stitch is a mistake)

From Double Knitting

Cast on the required number of stitches and do any foundation row. You need to have a number of stitches that are a multiple of two.

Do any edge stitches as the pattern calls for.
Knit one, tail is hanging to the back as with usual knit

From Double Knitting

Bring the yarn forward as if for a yarn over. You're passing it under the right hand needle so it hangs in the front as if for purl

From Double Knitting

Slip the next stitch, inserting the needle as if you are going to purl the stitch

From Double Knitting

Move the yarn to the back, passing under the needle again. The thread will cross horizontally across the slipped stitch

From Double Knitting

Knit the next stitch and repeat the slip across the row.

From Double Knitting

Row 2
Repeat the same process. The stitches you knit on the last row will now be slipped, and the previously slipped will be knit.
Knit

From Double Knitting

Pass yarn to the front

From Double Knitting

Insert needle as if to purl

From Double Knitting

Slip stitch onto the right hand needle

From Double Knitting

Pass yarn the back, across the slipped stitch and under the right needle

From Double Knitting

Continue pattern across row.

From Double Knitting

If you don't do any plain knit rows at the finishing end you have a one ended tube. You can castoff in a way that keeps this open.

From Double Knitting