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What is Offset Printing?

Offset printing is used to make labels for DVDs as well as to print the case covers.
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  • Edited By: L. S. Wynn
  • Last Modified Date: 27 July 2014
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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.

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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.

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kylee07drg
Post 7

@bijuchacko – I don't know much about commercial offset printing, but I can tell you a little about offset lithography in artistic printmaking. For starters, we draw on a metal plate with a litho crayon. This is a very greasy material.

When the drawing is complete, we put a solution of phosphoric acid and gum arabic onto the surface. This makes the drawing repel water while encouraging the ink to adhere to it. So, I would assume that the chemical used by commercial printers resembles this one.

Perdido
Post 6

I am a graphic designer, and at our firm, we use the PANTONE system to avoid any confusion with colors. Using a preset list of colors makes it easy for me to communicate with the printing department.

We keep a swatchbook of every PANTONE color in the office, and we let clients choose their colors from it. They can be sure that whatever they select will match the printed version of their ad.

Since the swatches list the percentages of each color, if we ever have to have something printed at another location, all I have to do is read off the CMYK percentages over the phone to the printer. This ensures that we are on the same page, because not everyone uses the PANTONE system.

orangey03
Post 5

I work at a newspaper, and we use offset printing on our press. The head press man in the back mixes the inks himself, and he always tells us to be sure our pages are totally ready when we send them to him, because once he burns the image onto the plate, it cannot be undone.

There was talk of switching to a direct-to-plate system, but we simply could not afford the equipment. I'm sure it would save money in the long run, but you can't buy something with nothing, which is about what we have in our budget.

babukandoth
Post 3

What is a blanket? how are they made? how many layers are available?

anon43516
Post 2

what are the blankets? How many layers are in them? What is the process to make them?

bijuchacko
Post 1

what chemical is used on the printing plate surface for the printing image?

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