I recently had a valued customer send me an email posing this question and decided that I would make it the next art term that I discussed on the blog since it is such a popular method for reproducing art work. One of the best description/definitions of the process I have found is below (courtesy of Wise Geek) as well as a bulleted chart of the advantages of offset printing as well (courtesy of Wikipedia).
What is Offset Printing?
Offset printing, also referred to as offset lithography, is a type of printing process used by virtually all large commercial printers. It is called offset, because the ink is not directly pressed onto the paper, but is distributed from a metal plate to a rubber mat where it is then set onto the paper.
Offset printing can be done on a web printing press, one that use huge rolls of continuously fed paper, or a sheet fed press that, as you would expect, uses sheets of paper. Both types of presses produce printed materials that can be cut to size after printing. Offset printing uses all of the latest technology in printing, including computers that aid in design. Computers are also used to generate instructions for the mixture of ink colors as well as their distribution to the paper.
Offset printing works because water and the inks used in the printing process do not mix. The images to be printed are created on the computer and then “burned” onto metal plates using a chemical developing process similar to photography. The metal plates are dampened with water which adheres to the areas without images. The ink is added next, one color at a time, where it sticks to the areas with images. The most modern systems use a direct-to-plate system in which the images are burned directly to the metal plates; the omission of a secondary step saves time and money.
The colors used in offset printing are usually Cyan, Magenta, Yellow and Black, represented with the letter K (CMYK). Note that K is used to represent black to ensure that there isn’t any confusion with blue. Different percentages of each of these four colors create virtually every color used in offset printing. There are color matching systems, such as the PANTONE® system, that allows print buyers to see the color. The code for that color can be entered into the offset printer’s computer and it will calculate the percentages of each color to be used.
The technology behind offset printing allows large volumes of printing to be completed quickly and without any variations in ink distribution. The final printed materials produced through offset lithography also dry quickly, keeping the production process moving smoothly from the printing to the finish work of cutting and binding materials.
The Advantages of Offset Printing
Advantages of offset printing compared to other printing methods include:
- Consistent high image quality. Offset printing produces sharper and cleaner images and type than letterpress printing because the rubber blanket conforms to the texture of the printing surface.
- Quick and easy production of printing plates.
- Longer printing plate life than on direct litho presses because there is no direct contact between the plate and the printing surface.
- The more you print, the less you pay, because most of the price goes into the preparation undergone before the first sheet of paper is printing and ready for distribution. Any additional paper print will only cost the client paper price, which is very minimal.
- High speed and high volume printing.