This stitch follows the same technique as a simple chain stitch. The only difference between the two is that a double chain stitch is done over two parallel stitch lines, instead of one. Thus, in the end, the visual effect is that it looks more or less like an open feather stitch.

To be able to do this stitch, it is good if you are aware of the chain stitch technique. I will be working on two straight parallel stitch lines, from bottom to top. All the stitch points will lie on the stitch line.

double_chain_stitch_1   double_chain_stitch_2
Fig 1: Bring out the needle through A which lies on one of the stitch lines. Put the needle in through B which lies horizontally opposite to A on the other stitch line. Peek the needle out through C and loop around the thread as shown.       Fig 2: When you pull out the needle, you would get a chain stitch loop with an open base. Now, put the needle in through A and peek it out through D to begin the next loop.
double_chain_stitch_3   double_chain_stitch_4
Fig 3: Loop the thread around the needle as shown.   Fig 4: Bring out the needle and tighten the loop. Continue this action of making loops with an open base on the left and right stitch lines alternately. The beginning of each new loop will be inside the previous loop on that respective stitch line.
Fig 5: A horizontal view of the finished pattern will look like this.