Useful Print Guide

Whether you’ve got nothing better to do or you’ve actually worked in print for years, I hope you’ll find this an invaluable guide to pre-press and print information.

So, if you’ve always secretly wondered what ‘CMYK’ actually is or perhaps a designer or printer has asked a technical question and you didn’t have a clue what they were talking about, then this guide will go some way to explaining some of the steps that are involved before, during and after printing.

This is a fun, easy guide to pre-press & print and is by no means an absolute definitive manual but it should go a little way to broach the everyday technical jargon you may come across, in clear concise terms. Also, it should act as a guide to save time, delays (and money) by asking the right questions to secure good quality artwork, resulting in a fast turnaround of the job. To see this guide as an online ‘flipping’ booklet that I did for a company called PTS, click here

How does printing work?

The basic principle on which it works is that oil and water don’t mix. A lithographic printing plate has non-image areas which accept water. During printing, the plate is kept wet so that the ink (which is inherently greasy) is rejected by the wet areas and adheres to the image areas.

Artwork is (nowadays) produced digitally and sent directly to an imagesetter to produce plates. When printing with more than one colour, separate plates are produced for each ink colour. In 4 colour process printing, 4 plates are produced (black, yellow, cyan & magenta - more of which later) - see diagram below.

Four Colour Printing Process Diagram

The 4 images at the top show how the printed sheet appears after each unit adds it’s colour.

The 1st sheet shows how the flower looks after running cyan. Then magenta and yellow are added in the 2nd and 3rd unit. Finally, the black is added and increases the depth of the final print.

The plates, which are flexible (usually 0.15 - 0.3mm aluminium) are then attached to the plate cylinder on the printing press.

During every cycle of the press the ink image is first transferred to a rubber surfaced blanket cylinder and from there onto the paper. This indirect method is called ‘offset’ after which the process is named. The blanket’s flexibility both preserves the delicate plate and conforms to the surface of textured papers for good results.

Cycle of the printing press

After printing, the sheets are taken for finishing - trimming, folding and binding.

The press can either be fed with paper, one sheet at a time (sheet fed), or from a large roll of paper (web - or continuous).

What on earth is image resolution?

The resolution is determined by how many pixels per inch an image has. High quality printed images must be at least 300dpi (dots per inch). So, a high quality image will have more ‘dpi’ than a poor quality image, as we can see with the image below on the left.

Images for websites are low quality images (usually 72dpi) and cannot be used in printing, see the image below on the right.

Image at High Resolution
Image at Low Resolution