Simon Leach teaches us how to do spiral fluting in this video. Start on the side of the bowl with a sharp edge. Then, push the edge down from the top until you reach the bottom half of the bowl. Create line next to line very close to each other, not overlapping them. Continue to do this slowly until you have reached all the way around the bowl. Make sure your lines are all equal to each other, they don't have to be perfect though. After you have made lines all the way around, your bowl will be finished and you can prepare it to fire.