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How can chemical ghosting be prevented?

On a recent book project we ran a flood satin varnish throughout. The printers were very careful to give the printed (b/w 1/1) sheets plenty of drying time before the varnish was applied; however, one side of the sheets were afflicted with sporadic chemical ghosting. It was explained as a reaction between the ink density and the varnish that only shows itself after the varnish dries. As a result there were areas within the pages where the varnish seemed to be imperceptible. The only clue as to why this was happening was that there were particularly dark areas that matched the form of the missing varnish printed on the reverse side of the pages.

Why is this happening and how can it be prevented entirely? My printers remedied the problem by running that side of the sheets through the varnish again after plenty more drying time. Almost missed my deadline on this one.

Ask the Experts #2

Submitted By

J S

Expert Replies

3

Topic(s)

On Press
Varnish

Look at it this way. It's gas trying to escape. Like everything in the universe, it takes the path of least resistance. If it can't simply evaporate into the open air, it'll go out the back door, through the paper, through the areas that have weakest barrier, the areas with the least amount of ink and coating. Once it's escaped, it leaves a mark of its struggle. It's kind of cool, isn't it? I mean, if you tried doing this on purpose. This evaporative process is part of every job. We only see the evidence when both sides of the sheet are flood coated without allowing the first side to dry. To avoid this in the future, you need to apply your newly gained foresight into your production schedule to allow the necessary time for both the ink AND the varnish to dry on the first side before you print the second side. Once, in a rainy season, I had to wait three days before we risked printing side two. — Patricia Benhmida, Genesis Inc.

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We ran into a very similar issue on a job last year that printed on both sides of the sheet with PMS 877 Silver, and two hits of PMS 295 (Dark Blue with a lot of Reflex Blue in the mix) with heavy coverage, and a flood varnish on a coated cover stock. We also almost missed the deadline as well. This year, we are getting ahead of the project by printing the 877 first and letting that dry a few days, print the double hit of 295 and let that set-up a few days, then come back with the flood varnish. The gas ghosting that occurred last year was interesting to see, as it was the silver image of the Nittany Lion Shrine that we have on campus. — Jim Lukens-Gable, Penn State Multimedia & Print Center

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I've seen drying racks with fans that disperse the air from above and below to allow for natural inconsistencies in the porosity of the paper. Also could be environmental. If the shop is humid, the ink won't set, thus the varnish will soak into the ink very slowly. — Troy Vera, EMC Advertising

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UnderConsideration is a graphic design firm generating its own projects, initiatives, and content while taking on limited client work. Run by Bryony Gomez-Palacio and Armin Vit in Bloomington, IN. More…