Lithography/Offset?
Out of context: Reply #8
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Gramme, you're right (see notes above).
I worked in a stone-litho studio for a while a million years ago. We used mostly real stones (they all come from the same quarry in Germany or Austria). Flexible 'Pronto-plates' were just being introduced at that time — you could print directly onto them in a laser printer or photocopier and then use special chemicals to set the image.
The advantage of stone is that you can reuse the stone literally thousands of times. You can draw directly on it using a variety of media; special crayons, inks, and so on. You can do some really nice graduated washes. When working in this way you can actually produce real graduation of tone rather than a line-screened (dotted) representation.
The disadvantage is that they gum up much quicker than plates, you can't really store stones for long periods of time because you generally need to have all your stones working for you rather than sitting on shelves. They're REALLY heavy (it's pretty dense limestone).
That's all primarily for artist prints and so on, not for actual reproductions from digital files. It's not really practical to photo-litho separations on to stone and run more than a couple colours.
Julien, the dots come from the line-screen that's applied to colour photos, etc, to create the illusion of more than just four colours; CMY and K. Line screen resolution is a separate discussion / issue.