As newspaper printing peters out with news-providers switching to digital platforms altogether, aluminum press plates are symbols of the traditional offset printing process. Offset printing is yet another notable improvement in the mass production of written work, allowing for not just hundreds or thousands, but hundreds of thousands of copies to be made and distributed.
A giant leap from the first printing press invented by Johannes Gutenberg, offset printing was the use of lithography which uses limestone instead of metal plates to reproduce artworks, for printing written works at a low cost. The first rotary offset printing press, made by Robert Barclay in England in 1875, used treated cardboard wrapped around its offset cylinder instead of the rubber used today. As photography developed in the late 19th century C.E., offset printing began to utilise photoengraving (the use of light to carve images onto metal surfaces) in the lithograph process, which leads us to the offset printing process of today.
Offset printing is based on the concept that water and grease do not mix. Grease-based ink is deposited on grease-treated areas of the printing plate while non-printing areas are coated with water which will reject the ink.
As a development of lithography, the offset plate is made with zinc or aluminum and coated with a photosensitive material onto which the negative of the page to be printed is placed and exposed to light, causing the photosensitive coating to harden on the areas to be printed. Modern offset printing requires four printing plates to be made of each page in each of four colours: cyan, magenta, yellow, and black (CMYK).
Offset printing machines are composed of three rotating cylinders and multiple rollers. The first cylinder is known as the plate cylinder, onto which the printing plates are fastened. This cylinder is followed by moist rollers that wet the non-printing areas of the plate and ink rollers which cause ink to adhere to the greasy sections of the plate. The second offset cylinder, covered in rubber, accepts the inked impression of the page and passes it onto the paper which travels around the final impression cylinder. Newspapers are printed in batches (print runs) on large rolls of newspaper which are then cut and folded by machine into individual newspapers.
Offset printing traditionally dominates commercial printing because of its ability to produce rich, accurate, coloured images and photographs as well as sharp typefaces and fine details for a price that drops with every copy that is printed—since the cost lies in the elaborate setup of printing plates and cylinders. The digital printer we know of today uses dry toner electrophotography to print which becomes expensive if it has to print more than 500 copies of the same page. Traditional offset printing, on the other hand, is designed to print thousands of copies of the same page, making it still the cost-efficient choice for newspaper printing today.
Bibliography
Bear, Jacci Howard. “How Does a Sheet-Fed Press Work?”. Lifewire, 2019, https://www.lifewire.com/sheet-fed-press-1074620.
Bear, Jacci Howard. “The Role Printing Plates Play in the Printing Process”. Lifewire, 2020, https://www.lifewire.com/printing-plates-information-1073825.
“Differences Between Digital and Traditional Newspaper Printing Explained – Newspaper Club”. Newspaperclub.Com, https://www.newspaperclub.com/choose/paper-types/digital-or-traditional.
“How Offset Printing Plates are Produced at Agfa”. Printing, https://www.agfa.com/printing/paper/printing-plate-production/.
“Offset Printing | Printing Technique”. Encyclopedia Britannica, https://www.britannica.com/technology/offset-printing.
Image Source
Yrithinnd, Offset Printing Process Diagram, 2009 https://en.wikipedia.org/wiki/Offset_printing#/media/File:Offset.svg Accessed 9 March 2021.
Prepared by Carol