Identifying printing processes, continued

When you say “rotogravure” most people have an almost reflexively say “National Geographic.” But many, many publications are printed by rotogravure. The benefits of printing by “roto” are significant, the most important being that the cost-per-copy of very long runs is low. To the National Geographic, however, it is a combination of cost and exceptional quality that causes that organization to choose rotogravure.

In a textbook on printing I edited for a major publisher there was a reference to roto which said that its primary advantage was economy. Economy on a press run of several million copies, they should have said. Rotogravure is, very obviously, not inexpensive. The cost of plate preparation is the reason. The National Geographic spends millions of dollars on every issue to make the cylinders that, once mounted on the press, allow each copy of the magazine to be produced at an “economical” price.

Rotogravure is different from the other types of intaglio printing – security printing and professional stationery. With roto, every mark on the page is made by the oscillation of a microscopic steel or diamond stylus that is used to engrave the cells into the copper cylinder on which the image is made (later chrome-plated). The diamond stylus chisels its image into the copper for both line work and for photographic work, and that is the telltale of rotogravure. If you look through a magnifier at the text of the National Geographic, you will see that the type is serrated by repetitive chisel marks of the engraving stylus.

The text in rotogravure is serrated by the oscillation of the engraving stylus. This is approximately 10pt. type.
Comparing roto to offset is easy, because the lettering on offset printing is sharp and clean – no serrations.

Offset printing does not impart the serration to letters (unless it’s imaged on a low-resolution imager) This is also 10pt. type, imaged on a Kodak Trendsetter, and printed on a sheet-fed Heidelberg press. And, comparing either offset or roto to intaglio printing is similarly easy. When products are printed by intaglio (sometimes called “engraving”) you can both see and feel the ink that is placed on top of the paper by the process.

This example of sheet-fed intaglio printing shows how much ink is put on the paper with this process. It is easily visible with a 10x or 20 x magnifier – and you can feel it. Hand an “engraved” business card to any printer and you can watch as they run a thumb and forefinger across the ink, then flick the edge of the card to take the measure of its caliper. “Engraved” printing has that effect on printers (and lawyers). If you could read their mind, you would hear, “Hmmm… must be at least fifty cents on this card! …sure is thick, must be at least 14 pt. stock…”

A curious effect of sheet-fed intaglio is that the impact of the plate on the paper crushes the sheet slightly, somewhat negating the thickness of the ink. You can often see the outline of the “die” on the paper (when it’s not done perfectly).

Some of the most valuable printing done on earth is done by intaglio. Currency and postage stamps are printed that way; it’s done to increase the difficulty of counterfeiting. It’s also done to make the currency last longer. That thick coat of ink wears better on nice linen paper than offset printing would.

If you want to have some fun, look at the new U.S. $50 bill and concentrate on what appear to be “lines” on the bill. Many of these lines are actually microprinting. You can read “United States of America” in several of them.