Crochet Double Chain (二重鎖編み)

I had my eye on a pretty capelet crochet pattern from this Japanese pattern book (Spring/Summer Handknit Collection for Women No. 7) for a few months, but didn’t have the right yarn on hand to start it until recently. So today I took a good look at the pattern, which is pretty straightforward: Use one strand of laceweight yarn, follow the chart, add the edging. Everything is cool except for this one instruction regarding the foundation chain:

スレッドの二重鎖編みから目を拾い、模様 編みで編みます。

I showed this to my mom (Japanese native speaker) who explained, “It says to make a double chain.” Eh?

I did a quick search through the book, which had diagrams for basic knit and crochet stitches plus a few specialty stitches, but there was nothing to explain the double chain (which isn’t the same as a double crochet, just to make things clear). There were around four or so other patterns that had this same instruction.

I decided to do a search of “crochet double chain” first, and found a video or two of the single crochet foundation stitch. Okay, that could work.

I searched for “二重鎖編み” next, and some of the hits included yet more videos of the single crochet foundation, but then there was this: http://i-s.milkcafe.to/ami/var/niju-c.html
I figured this was more along the lines of what the pattern intended, but it looked fiddley to work since you have to drop the left loop to work the right loop. Then I found another link where someone did this same technique using two crochet hooks at once. I gritted my teeth, found two hooks the same size, and tried it out. Super fiddley. By the time I got to the 6th round, it finally hit me: The construction of this chain is identical to a knitted 2-stitch I-cord. OMG! I can do I-cord so much easier and faster with a pair of double-pointed knitting needles or even a knitting machine than by juggling two hooks!

So the whole point of this is to say:

二重鎖編み = Crochet Double Chain = 2-Stitch I-Cord

That is all.