Here's the version from two years ago. I included Color Field Painting in the inspiration. Basically we used a blob of watercolor, and a straw to blow the blob into drippy shapes.
I needed a lesson that would review a lot of key terms and concepts, and introduce a new one, which didn't require a lot of demo and slides on my part. And I noticed as the next class came in, I didn't feel like demonstrating the exact same style of Op art. So I mixed it up with three different projects, all having simliar objectives: to demonstrate Value, Movement/Rhythm, Pattern, and (illusion of) Form.