Printing: The Offset Process

I think most people understand that you can't mix oil and water.  They are kind of like magnetic poles that repel each other.

These fundamental physical characteristics provide the basis for offset printing.



Plate and Blanket with Cyan ink

The ink which is made up of an oil based pigment - typically soy oil now days - is transferred from an ink fountain on to rollers that spread the ink evenly across a metal plate.  The plate has areas where the ink tries to stick - the image, and areas where water washes the ink away.  The remaining ink is transferred through a rubberized blanket to the paper.  On a newspaper press this happens very quickly - approximately 13 impressions every second for our press. 

Sometimes the ink overpowers the water and you see the result on a printed page.  It can appear as smudges around the edge of the paper, or a shading of the background - we call this scumming, or tinting.  If the water overpowers the ink, the ink appears light and "washed out" or disappears all together.  The paper can even stretch and develop wrinkles and other problems.

Ink and water balance is a huge part of high quality printing.  You must find that sweet spot where the ink and water, though fighting each other, work together to create a clean, vibrant image.

If you are printing black and white - this happens once on the sheet of paper.  When you print in full color, you now have Cyan ink and water balance to control, Magenta, Yellow and Black - all at the same time.  Not only do you need to control the ink and water balance on all four, but now you need to make all four of these colors line up on the page - called registration.  If a photo looks like a person has a second set of eyes, or you can see one of these colors "hanging out" of the photo frame, then the printing is said to be "out of register".

You can probably imagine how difficult it is to balance ink and water for four colors while simultaneously making sure the four colors line up precisely all while printing 13 copies per second!

Newspaper printing presses also use very thin paper.  Have you ever taken a magic marker and held it to a piece of toilet paper?  The ink spot continues to grow while you hold it on there.  What happens when toilet paper gets wet?  It loses its shape.  Those same things also happen to a lesser degree with newsprint.  The first time newsprint comes in contact with water it gets a little less stable and stretches.  That means the first ink you put on the paper actually grows slightly before the next ink is put on.  Fan out is the term we use to describe this process and there are methods to help control it, but thin newsprint compounds the complexity of printing four colors at the same time and balancing your ink and water.

Fan out, registration and ink and water balance is a problem for all presses and papers, not just a newspaper press. 

The next time you see a full color printed piece, now you'll understand a little more how much skill it requires to make it look that good.