GRAVURE CYLINDER IMAGING: The matter to be printed is reproduced on the cylinder as "gravure cells": small recesses which will carry the ink are engraved (electromechanically or by laser) or etched (chemically or by electrolysis) into its surface. Depending on the production method, the gravure cells can have the same area and vary in depth, or the same depth and vary in area, or both the area and the depth can vary. For typical publication gravure, the engraving process is used. Mechanical engraving normally takes place in a copper surface. Mechanical engraving uses tiny diamond styli oscillating up to 12 000 times per second. One mechanical engraving machine can have up to 16 engraving heads which work simultaneously, each covering the width of one page on the cylinder, to reduce the engraving time.
Laser engraving reaches an engraving frequency of 140 000 cells per second with two engraving heads, and uses zinc instead of copper. Both systems engrave cells in the cylinder surface, which depending on the strength of the electronic signal representing the image data, are correspondingly of larger or smaller volume.
In modern etching processes, the cylinder is first covered with a lacquer or photo-resist, which is then imaged by laser. The resist layer is removed where the cells are to appear. Computer-controlled spray-etching or electrolytic copper removal then generates the cells.