There are nine main types of printing processes:
- offset lithography - what we are exploring in this article
- engraving - think fine stationery
- thermography - raised printing, used in stationery
- reprographics - copying and duplicating
- digital printing - limited now, but the technology is exploding
- letterpress - the original Guttenberg process (hardly done anymore)
- screen - used for T-shirts and billboards
- flexography - usually used on packaging, such as can labels
- gravure - used for huge runs of magazines and direct-mail catalogs
Offset lithography is the workhorse of printing. Almost every commercial printer does it. But the quality of the final product is often due to the guidance, expertise and equipment provided by the printer.
Offset lithography works on a very simple principle: ink and water don't mix. Images (words and art) are put on plates (see the next section for more on this), which are dampened first by water, then ink. The ink adheres to the image area, the water to the non-image area. Then the image is transferred to a rubber blanket, and from the rubber blanket to paper. That's why the process is called "offset" -- the image does not go directly to the paper from the plates, as it does in gravure printing.
Now, let's look at the steps in the printing process.