Offset lithography is the most commonly used method of commercial printing. Known as the “workhorse” of printing, offset lithography is known for its high quality product, as well for its unique process.
The process of offset lithography is based on the principle that you cannot mix ink and water. The first step in the process is to transfer the document of text and/or images to film and plates. Digital files are transferred into film negatives, which are then transferred to printing plate. One of the determining factors in the final quality of the product is the choice of plate material. Paper, while cheaper, will produce a lower-quality product. On the other hand, aluminum, while more expensive, is the best material for a high-quality final product.
There are actually only four colors used in offset lithography (black, cyan, magenta and yellow) and each color has its own plate. The plates are first dampened by water rollers and then passed through the ink rollers. The water helps ensure that the ink is distributed only on the area where the image is located.
What makes offset lithography unique is the next step of the process. Instead of transferring the image directly to the final product, it is first transferred to a rubber blanket. It is then quickly transferred to the paper.
Once the image has been transferred, the paper is immediately sent through a special oven to dry the ink and remaining water in order to avoid the possibility of smudging. After the paper is dried, it is sent under “chill rollers” – rollers that have cold water running through them. This process cools the paper down and sets the ink into the paper so that it doesn’t rub off on your fingers.
The final stop of the process is the bindery. In the bindery the rolls of paper are cut and sorted into the correct order. At this point, your product is ready to be delivered.