For those who were unaware, the local Canberra Science Centre has a state of the art Harmonograph that is open for supervised access. It's a platform that creates a beautiful pattern of intertia against the friction of the pen onto a paper when pushed, ostensibly creating a much more complex version of what you might have seen from your Spirograph stencil kit as a kid! Here's a link describing how it works.
I've been teaming up with the friendly staff at Questacon to create a series of patterns containing perceptual constancy illusions and the 'McCollough effect' color illusion - and there's certainly an art to getting a fine overlapping pattern, not as easy as it looks at all. I'm working on a series of artworks with these images now for a future exhibit. Meanwhile I've been studying the human brain and visual-perceptual system, so needless to say it's been a real inspiration for looking closer at how we process images and artwork too.
Grapher software can create the same images digitally and also in 3D, though I've not tried the program yet. If you are interested in generating similar images to these, I would highly recommend checking it out.