Identifying printing processes

As a follow-up to my last blog on the Gap insert, I now have more information. This, thanks to sales rep Jim Sewell, who contacted me about the job.

I was wrong about it being sheet-fed offset. It was printed by web-fed offset, mea culpa, mea (minima) culpa!

According to Jim, the job was run in Los Angeles at Anderson Cenveo on their web-fed offset presses. Mr. Sewell continued, “The color was by Urban Studios, a great operation with a very talented full time color management person on staff.” The stock is Utopia II Matt 80# text. Mark Lassi, the head of Cenveo’s office in New York, is the account executive for the Laird and Partners account. Congratulations, again, on a stunning job!

Another person wrote, asking how I could tell it was printed by offset. And, that is today’s topic. Offset is very easy to identify, as are most other printing processes. All it takes is a magnifying glass (10 power is good; 20 power is better). Offset litho is indistinguishable from direct litho, but there is so little of that done that one can assume that it’s offset in today’s world.

When you consider how ink flows from a plate to the blanket to the paper in an offset press, the ink is quite cohesive, and it prints with little or no density variation near the edge of dots and small details. Thus, offset litho printing is exceptionally sharp and clear, even on irregular paper stocks.

This photomicrograph shows how nicely offset printing works on coarse (uncoated) paper. Notice how sharp the lettering is, a result of the offset chemical imaging process, very cohesive inks, and a blanket cylinder that absorbs microscopic paper inconsistencies.

If you compare offset to flexo, or any relief printing process, you’ll see immediately how to identify the two. Due to a characteristic called meniscus, the thinner inks used on flexo, and even the heavier inks used for conventional letterpress printing have a telltale density change near the edges of image areas. That phenomenon looks like this:
This is text printed by flexography, which is relief printing. You’ll notice how the ink density changes as it approaches the edges of solid areas. This is causes by meniscus, a factor in the flow of many liquids. I exaggerated the density of this photomicrograph to show those differences better.

…and this is approximately what that density looks like if plotted. A very similar curve could be drawn with conventional letterpress printing.
I’ll show examples of sheet-fed intaglio and rotogravure in my next blog. They are even easier to identify – one by touch, the other by image quality.