What is Offset Lithography Printing?

Howard Printing Co. has several Offset Lithography Presses, a process known for its sharp, clear images and quick printing speed.

Broken down into its roots, lithography means stone writing. The very first lithography prints were created using large, flat stones to transfer the image to the paper. The printing industry has come a long way since then!

When lithography was first invented, printers used stones to transfer the ink to the paper.

When lithography was first invented, printers used flat stones to transfer the ink to the paper.

In the printing field, a plate is the general term for the image carrier—it’s what carries the ink to the paper. For the first lithographic printers, the plate was the flat stone. For modern lithographic printers, the plate is a flat sheet of metal that is wrapped around one of the cylinders on the press.

You might be wondering how a flat surface can be used to print to only the correct places on the paper without spreading to non-image areas. The plate’s surface is treated so that it has two different surface types: hydrophilic (water-loving) and hydrophobic (water-resisting). The image area is hydrophobic, so it resists water and accepts only the oily ink. The non-image area is hydrophilic, so it attracts water and resists oil. When the press applies fountain solution (a mixture containing mostly water) to the plate, it only adheres to the hydrophilic areas. When the ink is applied to the plate, it is only attracted to the hydrophobic areas.

Offset is a term that refers to the way that the inked-up plate does not make direct contact with the paper. The ink is first transferred to a blanket roller, then to the paper. It results in a cleaner, sharper image.

Diagram of the cylinders in an offset press

Diagram of the cylinders in an offset press

The offset method was first put in use by a man named Ira Rubel in 1903. When his press missed a piece of paper and transferred the ink to the impression roller instead, the image showed up on the back of the next sheet of paper. Rubel noticed that this accidental image was cleaner and better than his directly printed images. He developed a press that utilized this extra step all the time. It had an additional roller called the blanket roller between the plate and the paper. Rubel’s offset method soon became the most established form of lithography printing.

Since its invention, Offset lithography has gone through many developments that have made it one of the most popular choices for the publishing industry. Today, offset is known for its speed and high quality at a relatively low cost, making it versatile for both small and large orders. Many magazines, books, newsletters, brochures, and labels are printed with the offset lithography method.

Susan Helmholdt
Western Michigan UniversityGuest Blogger
View Comments