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What Is Offset Lithography?

In offset lithography printing, plates carry both the image and non-image areas on the same level. The fundamental principle that allows the ink to capture the images on the plate is one that we all remember from our days in grade school - oil and water don't mix.

To create a print using offset lithography, image areas are photographically transferred to thin metal plates which are chemically treated to accept oil-based ink but repel water on the image areas. Conversely, the non-image areas accept water but repel the oil-based ink.

First, rollers covered in a clean solution, or water, are rolled over the plate. Then, a roller covered in oil-based ink runs over the plate, “sticking” to the images. The inked image is then transferred from the plate to a rubber blanket. The rubber blanket then transfers the image onto the paper's surface.

Because of the durability of the rubber blanket, it is possible to use offset lithography printing on a wide variety of surfaces and for large quantities. Lithography is commonly used for limited-edition runs of photographs. Both spot colors and CMYK colors can be used with this process. Offset lithography is also known as plantographic printing.

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