One of the many random hobbies I took up in grad school was drawing Celtic knotwork.
(I was reminded of this recently by Sideon's stained glass adventures.)
I used to joke around with my friends that this is the perfect hobby for me because it's Celtic and it's not work.
Hehe!! I'm such a jokemeister!!!
Maybe if I'd spent more time in grad school doing math rather than joke-smithing, learning French, and otherwise goofing off I'd be a Mathematician today rather than a code monkey... Ah, well, no sense worrying about it now...
Actually Celtic knotwork is naturally interesting to Mathematicians because there's something of a mathematical component to the knots.
At the time I picked up a book by a Mathematician giving an algorithm for how to draw Celtic knotwork based on mathematical principles:
I wasn't terribly pleased with the results I obtained with this algorithm. They were Mathematically correct but not aesthetically correct in that they tended to fill the space in a rather even and random manner.
So I went back to my earlier technique of just winging it...