This is an awesome tutorial from JoAnne at Oh Goodie Designs. It's even featured on the Martha Stewart craft site, so I had to share. I love making my own embellishments, and the ability to custom coordinate with a project is a crafter's dream. Photos and step-by-step instuctions below.
plain cotton thread (#10 crochet cotton works well)
markers (red & blue shown)
Tape one end of the cotton thread to the underside of your ruler.
Start wrapping the cotton thread firmly around the ruler.
Wrap the layers right next to each other with no overlap.
Continue wrapping until you reach the end of your thread.
Attach the end of the thread to the ruler with tape.
Starting at one corner of the ruler, begin to draw a diagonal line across the rows of thread.
I used a 2nd ruler (or straight-edge) to help guide my marker and keep my lines straight.
Press the marker firmly down and draw the line slowly.
You want the ink to saturate the cotton thread on both sides.
Move a 1/2 inch down or up, and draw another diagonal line parallel to the first.
Continue drawing spaced diagonal lines until the whole side is covered.
Flip the ruler over, and do the same.
Let it dry until the ink does not smear when touched.
Once dry, unwind and enjoy your homemade, custom-colored baker’s twine!