The basic principle of offset lithography is that ink and water don't mix. When plates are exposed, an ink receptive area is activated for the image. Water is applied to the plate and adheres to the non-printing areas and ink to the image areas. The image is transferred from the plate to a blanket which subsequently prints on the paper.

Offset presses are classified into sheet fed (run from cut sheets) or web (run from rolls). Sheet feed presses vary in shape, size and capability. Ranging from one to nine color units, and capable of inline coating, sheet sizes up to 60" (and larger in some cases), and much more, Essence maintains an assortment of sheet fed equimpment to meet the needs of the clientiele. Web pressess, because of their high speeds, are generally used for longer commercial runs and publications. Web presses are further classified as heat set, where the image is dried by passingthrough an in-line oven (principally used for commercial printin 

Web Size Designations
full web :: 38" wide
half web :: 22" wide
mini web :: 17" wide

Note: Publication web presses may have even larger plate widths. Most run both sides of the press simultaneously and offer in-line finishing options not found on sheet fed presses.