Offset lithography—one of the most common way to print ink on paper—uses printing plates to transfer an image to paper or other substrates. A printing plate is the surface which your design will be etched onto, usually made of aluminium. With the ubiquity of digital, offset lithography and printing plates may seem like an old fashioned method of printing but they have been standard in commercial printing for more than a century and continue to be so even with the increase in digital technology.
An image is put on the printing plates using a photomechanical or photochemical process during a stage of production known as prepress.
For a CMYK print one plate will be etched for each of the colours – cyan, magenta, yellow, black. During the printing process, this plate is inked up and a rubber drum rolls over the plate to pick up the image, it then transfers this image to the paper (or substrate). This will happen in four layers to create the full colour image.
In the past, the plate would be created by transferring a photographic negative to a plate that would be exposed in a dark room. With the progression in technology, the world of print has been able to combine old processes with the new. Today, the computer to plate system speeds up this process to etch directly onto the plate.
Why use printing plates over digital?
In terms of setup, printing plates / offset printing is much more expensive than digital printing, in fact digital printing has not setup costs to speak of. But the benefits of using printing methods are quite significant. Beyond producing a much more durable print, the image quality is noticeably better on paper and large runs can be produced at a far greater speed and cost.