Thanks again, @teditz ( When you brew your own beer and have a laser ) for the inspiration! I just finished labeling the mead (cyser, technically) I bottled this week. Laser-etched bottle caps courtesy of the `forge.
The image of the etched caps in the jig has the added bonus of being an accidental single-image stereogram.
So, my original intent was not yin-yang but, once it emerged, I just went with it.
I like the idea of using these sorts of spirals for butt joints, too. I started thinking about that as soon as I saw @evansd2 's first post on his experiments.