Zipatone is an obsolete graphic design material that would let you place a halftone dot screen across an area of a black and white illustration. Also marketed as Letratone, it came a thin plastic film with a slight adhesive over a backing sheet.
The dot pattern came in a variety of gray-tone percentages and in different sizes of dots, measured as lines per inch. The one shown here was a very sophisticated gradated tone.
The way you used it was to place it over your drawing on a light table, cut out the shape with a very sharp knife, carefully lift it, and place it over the drawing. For a very complicated shape, you could place a larger piece over the drawing and cut away what you didn't want.
There were a lot of pitfalls to those steps: cutting through the drawing, getting the stuff to fold up on itself, getting a speck of junk behind it, where it attracted a noticeable shadow. My memories of the stuff aren't that happy and glowing.
Previous Dead Tech post on waxers.