Offset Lithography
Offest Lithography is a process in which different types of surfaces play a big part. It is always printed on to a flat surface. An image is then transferred onto a printing plate. The printing plate contains two types of surfaces, the watery part and the waxy part. The waxy part reacts the the ink rolling across it and sticks to it. Where as the water based part cannot absorb ink, leaving a clean print.
Types of printing that use the offset litho process:
- General commercial printing
- Newspaper Books
- Business forms and legal documents
As you can see, this is a basic diagram of how the process works. The water rollers cling onto the parts of the plate cylinder that are non absorbant, and the ink, onto the waxy parts of the cylinder. They then roll onto the offset cylinder, which then reverses the image to back round the right way. The paper then rolls underneath the offset cylinder and the image is printed perfectly. It is called an 'offset' process, because the actual plates dont become in contact with the paper at any point.
Some of the benefits of offset lithography:
- High consistency in the quality of the printing.
- Its a quicker and easier process than others.
- Offset Litho printing is the cheapest way to produce high quality commercial prints.
Some of the disadvantages of offset lithography:
- The process of setting the plates, paper, ink etc is more time consuming than the other printing methods.
- Slightly inferior image quality compared to rotogravure or photogravure printing.
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