Offset Lithographic Presses and Plates

Today, offset lithograhic presses come in two main varieties. Presses can be either sheet-fed--paper is cut to size and feeds into the press one sheet at a time; or, web-fed--paper is on a large roll and continuously feeds into the press.

Today, most lithographic plates are made of aluminum sheets of varying thickness (usually between .008 inch and .0015 inch) with a surface grain or granular finish. This grain serves to give water-carrying properties to the plate and to give anchorage to the image forming material.

Upper right - A sheetfed lithographic printing press.
This press feeds in one precut sheet at a time

Lower right - A webfed lithographic printing press.
This press feeds paper continuously into the press from a large roll of paper.