Offset Lithography

Lithography works on the principal that oil and water doesn't mix. Unlike other printing processes that work by the ink either being applied to raised areas or pushed into recesses, lithography uses a smooth plate with oil or gum arabic to make hydrophobic (water repelling) regions that attract ink and hydrophilic (water attracting) regions that reject it. As the press runs, there is a roller that first wets the plate cylinder to charge the plate. It is then inked using the inking roller.

What makes the offset process different from standard lithography is that the images is first placed onto a blanket cylinder that then prints the image onto the paper. The advantage of this is that the soft rubber of the blanket creates a much sharper image than when the paper is printed directly from the stone or plate. Today, offset printing is the most common form of printing used in high-volume commercial printing.