WHAT IS OFFSET PRINTING?

Offset printing, also called offset lithography, is a method of mass-production printing in which inked images on metal plates are transferred (offset) to rubber blankets or rollers and then to the printing surface. The lithographic process is based on the repulsion of oil and water. The image to be printed gets ink from ink rollers, while the non-printing area attracts a film of water, keeping the non-printing areas ink-free. In offset printing, the paper does not come into direct contact with the metal plates.

Offset lithography became the primary form of commercial printing (replacing letterpress) starting in the 1950s. It is known for producing consistent high quality images and made printing in color more cost effective and more common. Subsequent improvements in plates, inks and paper have further improved offset printing quality and speed. Traditionally, film negatives were produced to make plates, but now most shops employ computer-to-plate workflows where printing plates are made directly from digital files.

Offset printing can print in both CMYK (or 4 color process) and Pantone (or spot color) inks. Unlike older letterpress presses, newer offset presses can print many colors at once. Shops now have presses that can print 4, 5 or 6 colors in one pass. Smaller, less expensive offset presses can often only print 2 colors at once. Offset printing offers the most flexibility for projects with special papers, special finishes and special sizes.

Since offset printing has relatively high set-up or front-end costs, very short runs can be cost ineffective. But since the set up costs are fixed, the unit cost goes down as the quantity goes up making offset printing still the most cost effective process available for medium to large volume printing.

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