Zip-A-Tone (aka Zipatone) was a widely used technique in graphic art, including comics, in the days before software-based art composition became commonplace.
It required the user to cut out pieces of adhesive-backed plastic sheets, with different patterns to each sheet, and pasting it into the comic page of interest.
It wasn't at all unusual to see Zip-A-Tone effects in black and white comics of the 70s and early 80s, as it was a way to impart eye-catching textures to a given panel or panels, as this impressive splash page created by artist Paul Neary for a 'Hunter' story in Eerie No. 55 (March 1974) shows:
So I was startled when, perusing the ever-shrinking comics pages in recent deliveries of The Washington Post, I saw that the strip 'Judge Parker' was employing Zip-A-Tone....!!!!
I'm guessing that 'Judge Parker' artist Mike Manley used a software app to render the Zip-A-Tone, as I'm guessing few, if any, sheets are still available.
It's open to question as to how many contemporary comics readers will even be aware of what Manley is doing with the strip. In my workplace of > 300 people, I am the only employee who brings a newspaper in to work........ With more and more comics being relegated to the 'online' version of national newspapers, I can foresee a day when comics simply are absent from printed newspapers.