How to Tell the Difference From Offset Printing & Gravure Printing
Offset printing and gravure printing are two of the four most important methods for turning ideas and words into books, newspapers, magazines and other printed matter. (Letterpress and screen printing are the others.) Offset printing, or lithography, is based on a rather simple chemical principle: Water and grease don't like each other, so the printing plate repels water-based ink everywhere, except where you want the ink to print. Gravure, or intaglio, uses an etched metal plate (lithographic plates are flat) to hold the ink, which is then impressed into the paper. You can tell the difference between gravure printing and offset printing with a hand magnifier and a little practice.
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Instructions
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Hold the printed page in one hand, and examine the page closely with the magnifier held in the other hand. Focus in on the individual letters. Look for letters with smooth, sharp edges in all parts of the letter -- those are offset printing. Look for letters that appear to have small serrated edge patterns, like the teeth on a steak knife -- those are gravure printing.
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Turn the page over and examine the back. Run a finger across the page. Offset pages will be smooth. Gravure printing, however, forces the paper into the recesses of the etched printing plate, so there will be tiny indentations on the back of the page.
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Turn the page over and run your finger over the printed material. Offset printing will be smooth, and you'll probably smear the letters slightly if you rub them hard enough, though you may need the magnifier to see this. Gravure printing will have raised letters, like Braille printing, and is much more smear-resistant than offset.
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Tips & Warnings
Letters made by letterpress printing, when seen under the magnifier, appear to have a heavier edge of ink around the letter, caused by the plate pressure on the paper. The page also may be dented or even embossed on the back, from the letterpress type pushing into the page.
Screen letters will appear to made up of tiny boxes.
If the printing, to your finger's touch, appears to be raised, but the back of the page is smooth, chances are you have a letterpress page using a process called thermography, which heats ink and a powder to make raised letters -- much cheaper than the real gravure work you find in fancy wedding invitations.
References
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