The Thumb Method of Casting On

This method of casting on, is quite different from other methods of casting on.  For this method you start casting on part way through the ball off wool.  The amount of wool you require for casting on is determined by the number of stitches you require.  As a rule of thumb with double knitting wool approximately 14 inches of wool (36 cm) is sufficient to produce about 25 stitches.  Again the cast on is started with a slip knot but all subsequent stitches are created by winding the wool around your thumb and then knitting the stitch from your thumb onto the needle.
Personally this is my least favorite method of casting on simply because I find it is difficult to estimate the amount of wool required to cast on.  However a lot of people really like this method, because it is easy to control the tension on the needle as you cast on and it produces a nice neat edge to the work.  Try it and see if it works for you.

1.

Form a slip knot on the wool, allowing sufficient wool on the free end of the wool to make your stitches.  (Approximately 14 inches per 25 stitches for DK). 
2.
Place the slip knot on the right hand needle.  Take the free end of the wool with your left hand and wrap the wool one and a half times around the thumb on your left hand.
3.
Using the needle in your right hand place the tip of the needle through the loop on your left thumb.
4.
Using your right hand and the wool feeding from the ball, wind the wool around the needle in an anticlockwise direction.
5. Pull the needle back through the loop on your left thumb and remove it from your thumb.
6.
At this point you will have two stitches on the right hand needle and the free end of thread and the loop from your thumb in the left hand.
7.
 To complete the stitch, drop the loop and pull the free length of wool to remove the loop.  Repeat steps 2 to 7 until the required number of stitches are on the needle.