When I started learning tatting this was a non-existing technique. Learning the technique, I understand way.
This technique came from a different type of knot, known as the lark head knot. When looking at the result of the knot you see the double stitch. This knot is create then the thread is folded in half, creating a loop to pull the ends of the thread through, there the thread is looped around something. (A)
The first type I have learned how to do this knot was to have the core thread needed in the double stitch; will be the picot to where you will be joining. The chain is the only technique used in the lark head picot join.
Where you need to make a join, make the first half of the double stitch by pulling the thread thought the picot you want to join, from behind (B), putting the shuttle through the loop. Pulling the loop though the picot (C) and pull on the new loop, placing the shuttle though that loop (D), by pulling on the shuttle thread you close the loop and complete the join.
During a tatting, session I found out a little secret shortcut in the lark head picot join and I use this trick in my rings when I am tatting jewellery to add a clasp or small metal rings. I gave the join to much slack and it undid itself (E, F).
The second type’s first method is to pull a loop through the picot (G), creating the double stitch without the core thread (H) and placing the shuttle through the loops.
The second method it to pull the loop through the picot, twist it (I) and place the shuttle through the picot. First half of the double stitch is done and now for the second part of the double stitch. By pulling for the second time a loop through the picot allowing the loop to twist itself so you can see the double stitch form (J) placing the shuttle through the loop.