The Offset Litho Process
On a good day, offset litho printing works as follows. Paper is loaded onto a platform at the back end of the press, above which is a series of suckers. These lift the paper, one sheet at a time, and enable the grippers (grabbing pincers mounted on a chain-link drive) to grab it along one edge (called the gripper edge) and pull it into the first ink unit, where it is printed with the first color. As it leaves, it is grabbed again and pulled forward into the next ink unit, and so on.
Presses vary as to how many ink units they have. Book presses typically have just one ink unit in order to print only black text, and are often very large format to allow many pages to be printed together on a big “parent” sheet.
Presses used ...