You'll need a string of pearls, any size will work, I used 6.5mm-7mm cultured pink pearls.
small beading needle
cotton crochet thread size 20 (or 10 is you have larger pearls)
tatting needle size 7 (or 5 if you're going with big pearls and size 10 thread)
Basic needle tatting knowledge is needed and can be acquired in my learn needle tatting instructable.
Step 1: Dismantle Pearl Necklace
String them all on even though you may not want to use them all, there is no cutting and tying until the end of the necklace.
Step 2: Getting Started
Step 3: The First Pearl
Place the needle on the pearl and start the first chain. I chose to do 15 ds between each pearl, but you can chose to do more or less to create the look you'd like. Close and tie.