How does rotogravure use differently etched squares to reproduce shades of gray?

In rotogravure printing, shades of gray are reproduced not by varying the size of the dots, but by varying the depth of the etched cells.12

The process utilizes a gravure screen—a grid of intersecting lines—to create thousands of tiny, equal-sized squares on a copper plate. During the photomechanical transfer, the plate is exposed to light through a positive transparency of the subject. The emulsion on the plate hardens in proportion to the range of grays in the image.12

When the plate is subjected to an etching bath, the acid affects the squares differently based on the hardness of the emulsion:
* Deep cells: These hold more ink and produce darker tones.12
* Shallow cells: These hold less ink and produce lighter tones.12

Because these cells vary in depth while remaining the same size, the process can replicate a rich, continuous range of tonal values, making it highly effective for intaglio reproduction of photographs and detailed artwork.123