Following link to a video version, as posted by Normand.
http://youtube.com/watch?v=RT-sMgqZoDI&feature=related
I cannot take credit for the idea, just the pictures and post The white rubber pieces are from a cheap bungy strap.
Step one: Clamp the rubber material in your vise securely.
Step two: pull the rubber tight, and spin the rubber leg material, or your vise (if you have rotary) until releasing pressure slightly causes a similar twist as shown.
Step three: Once again pull the rubber material until it is tight and no twists are visible. Then Apply the color of your choice with a permanent marker. Going over it repeatedly can lessen the barred effect and pattern. A single stroke along the length of the rubber will create the most uniform barring.
Amount of twist, tension, and number of times you go over the rubber with the marker will all vary the effects. Experiment a bit to find what works best for you.