The offset lithographic process works by first transferring an image photographically to thin metal, paper, or plastic printing plates. Unlike other forms of printing, in offset lithography the image on the printing plate is not recessed or raised. Rollers apply oil-based ink and water to the plates. Since oil and water don't mix, the oil-based ink won't adhere to the non-image areas. Only the inked image portion is then transferred to a rubber blanket (cylinder) that then transfers the image onto the paper as it passes between it and another cylinder beneath the paper.
The term offset refers to the fact that the image isn't printed directly to the paper from the plates, but is offset or transferred to another surface that then makes contact with the paper.
Doing Offset Printing
- How Offset Differs From Desktop Printing - The three primary differences in offset printing and desktop printing (such as inkjet and laser) are the colors of ink and the way the ink is placed on the paper as well as the type of machinery used to accomplish the task.
- Preparing Files for Offset Printing - When you send a digital file out for film or printing more goes along than just your PageMaker or QuarkXPress document. You may need to send fonts and graphics too.
- Book Paper - Offset papers are especially suitable for offset printing due to increased resistance to water and picking. Most book paper can be used on offset presses.
- Printing the Color White - Most inks used in offset printing are translucent therefore a translucent white ink would not cover a dark color. Explore your ink and printing options are for printing in white.
