Video: Expanding Blue Ring (CAN)

Thanks to Bob Greenyer for bringing attention to a video by CAN, an active experimenter. This is a very short video which shows an interesting effect. On the YouTube description he writes:

An interesting effect can be triggered by collecting a ball of electrolyte on the anode and striking it on the jar wall, which is weakly electrically connected to the cathode. A ring with a deep blue-violet color slowly expands from the strike point.

K2CO3 electrolyte concentration was about 0.4M. 600V across both electrodes; the jar is not completely insulated from ground.