What is commonly referred to as “offset lithography” is a method of printing which is put to use all around the world. The majority of books, newspapers, magazines, brochures and pamphlets have all been printed using offset lithography.
- This printing procedure is globally regarded as the mainstay of printing, due to its fast, effective, affordable, and relative ease of use.
The word “offset” in the name is attributed to the fact that the ink is moved to a separate area before it is applied to the paper.
The first stage of offset lithography is producing a plate with the image which is to be printed. Should the image be a black and white one, only a single plate is necessary, because the plate can easily be inked with black ink.
All colour images are made by way of using a four colour separation process, in which four diverse plates are made for the yellow, cyan, magenta, and key (black) inks.
- When the plates are being printed, the colours will merge together visually, and thus create the wished for colour image.
- Anyone seeking the best in high quality litho concentrates coatings, should contact renowned specialists in the pigment dispersion business.
The Use of Photo Sensitivity
The plates, which are used in offset lithography are completely flat, and in contrast with the textured surfaces of any engraved plates and movable type.
- These are manufactured by generating a film negative of the image, and then placing it over a photo-sensitive plate, which then exposes it, and then develop it. After a plate has been made, it can then be mounted in a press, and hey presto, the magic begins!
This method of printing takes great advantage of the fact that oil and water do not mix. The plate is swept with rollers which have been coated with water, and then with other rollers covered in ink. The ink clings to the parts of the plate which were exposed earlier on, whilst the water keeps the unexposed parts clear so there’s no smearing or transferring of ink.
The plate will then transfer the ink to a rubber roller called a “blanket,” and this then rolls over the paper. The paper is then fed between the blanket and yet another roller to make sure that the image remains nice and crisp.
A Workhorse Indeed
The offset press itself can run continuously, making it exceedingly fast. Depending upon what the type of job is, the press will be either sheet fed:
- Meaning that singular pieces are pulled from a stack by the press and then run through
- Where the paper is on large rollers.
In each case, the paper will be run through an oven after being printed which helps it to dry faster and prevent smearing. It is then ready to be cut, bound, folded, and made ready for immediate distribution.
The next time you pick up a magazine, think of all the thought and work which was put into it!