Offset lithography is a fast, efficient, and cheap printing technique used for books, newspapers, and magazines. It involves making a flat plate with the image to be printed, which is then transferred onto paper using rollers covered in ink and water. The process can be sheet-fed or roll-fed and produces high-quality images. The first offset lithography press was developed in 1903 and has since become widely used in the printing community.
Offset lithography is a printing technique widely used around the world. Most books, newspapers, and magazines are printed using offset lithography, and this printing technique is widely considered the workhorse of printing, because it’s 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 black and white, only one plate is needed, 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 cyan, magenta, yellow, and key (black) inks; when the plates are printed, the colors blend together visually, creating a full-color image.
Offset lithography plates are entirely flat, in contrast to the textured surfaces of engraved plates and movable type. They are made by creating a film negative of the image, placing it on a photosensitive plate, exposing it, and then developing it. Once the plate has been made it can be whipped up in a press and the real fun begins.
This printing technique takes advantage of the fact that oil and water do not mix. The plate is brushed with rollers covered with water, then with rollers covered with ink. The ink is attracted to the previously exposed portions of the plate, while the water keeps the unexposed portions clean so they don’t smudge or transfer ink. Then, the plate transfers the ink onto a rubber roller known as a “blanket,” and the blanket rolls up onto the paper; typically the paper is fed between the blanket and another roll to ensure that the image remains sharp.
An offset press can run continuously, which makes it extremely fast. Depending on the job, the press can be sheet-fed, which means that individual pieces are pulled out of a stack from the press and fed, or roll-fed, in which case the paper sits on huge rolls . Either way, the paper is typically run through an oven after printing so it dries quickly, avoiding smudging, and then can be cut, bound, folded, and prepared for distribution.
The first offset lithography press was developed in 1903, and the concept quickly caught on in the printing community. Offset presses range in size from the huge presses used in commercial publishers, which can be larger than a house, to smaller models the size of dump trucks used in smaller printing companies.
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