What is Offset Lithography?
Offset lithography is a printing technique which is widely used around the world. Most books, newspapers, and magazines are printed using offset lithography, and this printing technique is widely regarded as the workhorse of printing, because it is fast, efficient, cheap, and relatively easy. The “offset” in the name refers to the fact that the ink is transferred to a separate surface before being applied to the paper. The first step in offset lithography is making a plate with the image to be printed. If the image is in black and white, only a single plate is required, because the plate can simply be inked with black ink. Color images are produced using a four-color separation process, in which four different plates are made for the cyan, magenta, yellow, and key (black) inks; when the plates are printed, the colors blend together visually, creating a color image. Plates in offset lithography are entirely flat, in contrast with the textured surfaces of engraved plates and movable type
Lithography is the process of imaging from a flat surface. Offset is the process of imaging one surface, and then offsetting the image to the paper. Combined, Offset Lithography is the process of achieving a printed image from a flat surface, once printed on an intermediate medium, and then transferred to the paper. This process is vastly different from letterpress (Raised Image), Flexography (Raised flexible image), Gravure (engraved image), Silk Screen (Pores on a Silk Screen) printing – The image and the non image are flat and the inked image is formed from the basic principal that ink and water do not mix. Ink being an oil base and water are opposites. The image on the litho stone or flat surface (modern printing plate) is achieved through a photographic or digital means. The ink receptive areas are treated chemically to attract oil based inks, whereas the non image areas are chemically treated to receive water (or non oil based liquids). The printing process is cyclic where the pl
n offset lithography (also known as plantographic) printing, plates carry both the image and non-image areas on the same level (unlike letterpress where areas are raised to catch ink). The transfer of ink is controlled by an unlikely principle. The principle that oil and water don’t mix. Image areas are photographically transferred to thin metal plates which are treated chemically to accept oil-based ink but repel water on the image areas. Conversely, non-image areas accept water but repel the oil-based ink. A plate first contacts rollers of a clean solution or water and then is inked by other rollers. The oil-based ink “sticks” to the image area. 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 resilience of the rubber blanket, it’s possible to use offset lithography printing on a wide variety of surfaces and for large quantities. Both spot colors and CMYK colors can be used wit
