Here are nine scans for a step by step look at how to create the tatted split chain.
The following directions for creating a split chain cover the following situation: You have been tatting a chain which was joined somewhere to the left and you have continued tatting to the right up to the mid point of the chain. In this position the right side of the chain in progress is up or towards you. The chain would have finished and been anchored somewhere to the right if completed in the traditional manner.
Instead you are going to measure out a length of thread equal to the chain just completed, attach it to the right and wrap thread over the bare shuttle thread back towards the left to the mid point of chain and then climb out of the round with a mock picot and either a split ring or a chain.
Nota Bene: If the wrong side of the work is towards you or the chain is headed to the right and needs to be anchored on the left, these directions must be modified by starting the stitch/wrap on the opposite side as given below.
The most important point of this technique is that it should be done slowly. The thread is wrapped around the anchored shuttle thread in two stages both of which must be done loosely and then the two halves of the stitch slowly tightened one after the other. Do not tighten the first part of the stitch before the second part is done.
You are tatting a chain from left to right. Tat up to the mid point of the chain (or that point where the mock picot or split ring would attach; it does not necessarily have to be the exact center of the chain.) Scan A
Measure off a length of shuttle which is slightly shorter than the length of chain needed. (It is shorter because in the process of wrapping the thread this portion of the bare shuttle thread oftens stretches.) Anchor the measured length at the point where the chain normally would have finished. Scan B
Looking at the chain, the completed chain is right side up and on the left while the bare thread is anchored and on the right.
1. Let a loop of the shuttle thread drop behind the bare thread. Scan C
2. Bring the shuttle to the front over the bare thread and into the loop thus formed passing the shuttle over the left side of the loop and behind the right side of the loop.
3. Gently pull the loop towards you and upwards a little. Gently tighten a little. Scan E
4. Bring the shuttle to the back behind the bare thread and into the loop thus formed passing the shuttle behind the left side of the loop and over the right side of the loop. Scan F. Then see Scan G: Tighten gently by pulling shuttle thread down Scan H
5. Return to the first loop and gently pull one side only until it moves to the right and touches the anchor point. Gently pull the other side of the loop into place. Then rotate the stitch upwards on the chain thread. As you pull you will see the "legs" of the double stitch and the "bar" of the double stitch move into position. Tweak each side until the tension is correct. Scan I
If it does not look like a correctly made double stitch, follow the shuttle thread to take it out and try again. If all is correct go onto to make as many of these ds as necessary to reach the midpoint of the chain.
The split chain allows you to climb from the center or from one round to the next without cutting or tying the threads.
This technique is called the split chain or bridging. It was originated by Dora Young. See her book