This is a pretty simple technique, which is almost like a spiral filling, except it's a parametric (a simple one that is close to a spiral). The idea to render something monochrome with a parametric is interesting, I would like to dig more in future. I also tried it on typography (for a family gift).
This plot is done with fountain pen and ink "Amber" by Diamine, which I really like.
When you look closer, there are high frequency noise used to make it more fuzzy.