Lithography/Offset?
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- JulienDonkeyBoy
Hello there,
Once again with a basic question:
Would someone please explain the difference between Lithography and Offset printing?
- ********0
- MrNibs0
Agreed. Google is quite useful for finding answers... and porn.
For kicks I will attempt to explain while horribly plagiarizing the interweb. Do correct me if I'm missing something.
Lithography is a process of creating an image without raised or engraved surfaces like letterpress or rotogravure. The image, both negative and positive, exist on the same plain and use a chemical process that allows ink to adhere to only the parts of the surface to be reproduced.
Offset printing just refers to the plate transferring the artwork to an intermediate surface (a rubber blanket) before making the final impression on the paper.
They are often referred to as one in the same because essentially an offset press uses a lithographic process to produce the image. However, the lithographic process does not require an offset press to produce the image and can be directly transferred to a paper surface.
In short, one is a process for producing a plate and the other is a technique for transferring the artwork from the plate.
- It's all based on the fact that oil and water don't mix. The image is placed on the stone (litho) in oil and then wetted...********
- ...the oil-based ink is rolled over and only sticks to the oil on the stone, not the wet parts.********
- The image is then transferred either directly to the paper, or offset on a blanket (offset) and then to paper.********
- awesome
JulienDonkeyBoy
- It's all based on the fact that oil and water don't mix. The image is placed on the stone (litho) in oil and then wetted...
- JulienDonkeyBoy0
I'm kind of confused, can you tell the difference when you see the final product?
- This is how it is done (old school) without an offset press. http://www.youtube.c…MrNibs
- Hey, good find.********
- See Julien, Google is your friend.MrNibs
- JulienDonkeyBoy0
bump
- Dots are the final product in both.********
- thanks man very helpfulJulienDonkeyBoy
- You get dots b/c the image is pushed through a screen, unless it's a solid spot color.gramme
- Dots are the final product in both.
- gramme0
MrNibs is right. Offset printing is the way lithography is done in commercial printing. So, offset printing = offset lithography = lithography. All the same thing in terms of results. Again, offsetting is merely the usage of a blanket to transfer ink from plate to paper.
- gramme0
Hand-produced lithography uses an actual stone and no blanket (to my knowledge). This process is really only useful for art prints and very limited editions. Not useful at all for commercial work.
I would imagine that even with a skilled hand, old-fashioned lithography wouldn't look nearly as crisp as modern offset litho. I don't really know much about the old process, so I'd better shut my gob at this point.
- JulienDonkeyBoy0
What dictates the amount of dots? higher quality=more dots I understand...
- Depends on the line screen. You're right about more / smaller dots = better result.gramme
- ********0
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.
- JulienDonkeyBoy0
Pylon, I'm about to cry... haha now I understand much more.
How are the plates made? Iheard there are Digital Plates and plates that come from Negatives... I/m confused about that too.
All these questions come because I have a true desire for learning all the process of printing and be able to achieve amazing quality for my future work...
thanks for all your help
- ********0
It's all in here my dear:
http://en.wikipedia.org/wiki/Lit…
http://en.wikipedia.org/wiki/Off…
- gramme0
Julien, digital plates are used in DI (Direct Imaging) presses, HP Indigo (digital offset) presses, and contemporary offset lithographic presses. In the first two instances, the image is transferred directly from the computer to printing plates that are pre-installed or pre-hung inside the press. In the third instance, the image is transferred directly to plates that are *then* hung on the printing press. This latter approach is how most commercial printing is done these days.
There are still some printers, mostly small shops, who use negatives to transfer art from computer to plate. This is a photographic process that burns the image onto a negative which is then transferred to the plate. This process is quickly disappearing, as the digital way is quicker, more efficient, and uses fewer materials and fewer chemicals.
- Actually I should say, in the third instance the plates aren't digital, but the computer > plate transfer is.gramme