We’ve been talking about joins for a while now, and we’ve already got a bunch of options. But, because you can never have too many options (or skeins of yarn), I’ve got one more for you. It’s at the upper end of fiddly-ness scale, but in specific instances, it’s totally worth it.
Check it out:
Unravel three or four inches of the end of your old yarn. (This works best with multi-plied yarn, rather than single-ply.) Separate the plies out. Leave the new yarn intact.
Take a thin tapestry needle and carefully sew each of the plies one at a time into the end of the new yarn. 
Try to sew the plies into the new yarn along different paths, weaving them together to form a nice, sturdy join. Be patient with yourself; this can be tricky to do. 
Pros: This join results in an invisible transition (no ends to weave in!) that doesn’t rely on getting spit everywhere. This join also works really well with non-feltable yarns (like acrylic and cotton).
Cons: Probably the most complicated and tricky join we’ve talked about. It doesn’t work super well with single-ply yarn (but you can make a bitchin’ spit join with single-ply wool).
On the Needles 