Untitled (zebra scallop/clamshell)

This image was created using the same formula that I used for the Guilloche Spiral. From the inside out, the boundary curves are rose curves of increasing numbers of petals, from 1 to 20. Between each pair of curves, the spiral completes one turn. Then, I added another series of spirals going the other way, which created a series of discrete areas of roughly concentric rings. I filled every other ring with solid black, making the overall image black on white.