My son was watching “Mighty Machines” (from 2008) where they explain the process and the equipment involved for making 600,000 newspapers. They explained how plates are made from which the printed image is pressed onto the newsprint paper. However, I noticed the plates are NOT the mirror image of the printed image. Why not? How is that possible that the plate AND its image are not mirrored versions of each other?
Depends on the machine. In some cases they are the mirror image.
However, in the ones you saw, the plate will be dipped in ink, then run across a smooth roller of something mildly adherent. The roll is then run across the paper, before being cleaned by a process like a squeegee. The middle step smoothes out bubbles and gaps in the ink.
Since there are two transfers (plate to imaging roll, imaging roll to paper), the plate is a straight image.
What always amazes me is that even in this technological age, almost all printed materials (even super high-zoot intaglio stuff like currency) are produced with basically “rubber stamp” technology: dip something in ink, shove it against the paper. It wasn’t until the inkjet (squirt it on) and laser/xerographic (bake it on) that we moved to anything else, and high-quality stuff is still basically stamped.
Thanks, TimeWinder. Following up on what you explained, may I ask: I thought xerography was done by static electricity. Is baking (or, perhaps some kind of thermal process) an option? Also, is xerography impractical and/or not economical for large scale productions?
It’s both: the toner is deposited on a roll or directly to the paper electrostatically, but it’s usually still powder at that point and needs to be “fused” (basically baked and melted) to stick to the paper permanently. Hence the “fuser” unit that’s separate from the toner cartridges in some printers: it’s usually a hot wire, but the technology can vary.
There are large-scale laser presses, and for that matter large-scale inkjet presses (I worked on programming for one of these, a few years back). Both technologies are used for on-demand type stuff ( each page out of the press might be different) where printing plates would be cost prohibitive. But for volume work, they’re not economical (or weren’t, when I was last in the biz). You will never meet a more frugal bunch than print professionals; their margins are (pun unavoidable) paper thin for most jobs.
There’s screen printing. Lithography is also stamping, although it isn’t based on protrusions on the surface of the stamp.
If they are not, it’s because there is an intermediate step. That’s why it’s called “offset.”
To answer the question of why the “rubber stamp” concept is used instead of inkjet, dot-at-a-time, it’s because a plate pressed against a piece of paper conveys an enormous amount of information in a short space of time with very little effort. The technology necessary to point a laser beam or an ink jet at a single, small dot, then repeat it supersuperfast, is highly complicated compared to a simple plate. Plate pressing technology is two or three hundred years ahead of laser beams.
I’m sure they will catch up.
For something like newspapers, it’s the only technology available for producing at volumes like a million pages per hour. - See: http://www.youtube.com/watch?v=-kEV7QZn_CA
ETA: What musicat said. This is the cutting edge.
Printing plates are an example of where analog technology prevails: once you’ve invested in the comparatively slow setup process, the execution is lightning fast.
ETA: although I wonder if a configurable dot-matrix printing plate would be practical.