Photo purchased from … www.depositphotos.com
Thirty years ago I was promoted from designing print books to serving as the art director and production manager of a government education nonprofit organization. When our best designer got a new job, I took over all of her promotional design work and learned to use Quark XPress (page composition software). It was one of the more intensely educational periods of my professional life.
One of the promo items I produced was a 16-page catalog on 70# gloss text with a 100# gloss text cover. The tall and narrow format was approximately 6 1/8” x 10 7/8”. It was a saddle stitched, four-color product with a press run of between 40,000 and 60,000 copies. The nonprofit was flush at the time, and marketing was viewed as an investment. Also, it was before the wide use of the internet for marketing.
To get back to the size, we chose an odd format because it just fit the US Post Office’s definition of a letter. Anything larger (even 1/8”) would have been a “flat” and would have cost more to mail. But in addition, we chose the size because it fit exactly within the roll width and cut off of the heatset web press owned by one of our best commercial printing suppliers. (More specifically, eight pages of the catalog fit exactly on each side of a sheet cut from the web roll, allowing room for bleeds and printer’s marks.)
And for such a long run (the number of pages multiplied by the press run), producing the job on a heatset web was faster and cheaper than printing the job on a sheetfed press. Moreover, since it was produced on gloss stock, we needed a heatset web rather than a non-heatset web (because we needed the ovens to cure the ink through oxidation). So this was exactly the right custom printing press for the job.
Proofing and Dot Gain
When I started regularly checking proofs for this catalog (a repeat job produced every six months), the first thing that struck me was that the proofs were too light. The b/w halftones, the 4-color images, the area screens, everything. At first I was upset, and then the printer explained to me that heatset web presses have higher than usual dot gain, so the separations need to be “opened up” or burned to negatives, proofs, and plates with lower density, so the final printed product would look as I had intended it to look. (We still used negatives back then.)
So I went to school on the subject.
“Separations” were the four sets of negatives and plates, one set for each of the process colors: cyan, magenta, yellow, and black. “Opened up” meant that the halftone dots of any of the process colors would be reduced slightly in size. And “dot gain” meant that certain types of presses, certain printing processes, and certain types of paper will result to a greater or lesser extent in the enlarging of halftone dots on press. (This is also known as “tone value increase.”)
And the heatset web printer’s solution (opening the separations) was the correct approach to eliminate the dot gain problem.
How Does Dot Gain Present Itself?
In the case of my employer’s catalog of government education print books, the overall darkening of all colors that would have occurred had the printer not opened up the separations would have been the result of the dot gain.
But this is not all that can happen.
According to my go-to book on printing, Getting It Printed by Eric Kenly and Mark Beach, “Halftones and separations lose detail, colors shift in separations, screen tints print too dark, color builds don’t match swatches, chokes and spreads [trapping] don’t function properly, and fine lines drop out when printed as reverses” (Getting It Printed, page 65).
How Is Dot Gain Measured?
According to Getting It Printed, if you start with a 50 percent dot and you have 10 percent dot gain, the halftone dot would now be a 60 percent dot (50 plus 10, not 50 plus 10 percent, as I understand it). Unfortunately, dot gain can be different in different screen percentages of a printed product, since different sized halftone dots grow in different amounts (smaller dots grow more than larger ones, for instance).
Plus, if you think about it, the art file for a double-page spread of one of your commercial printing projects, let’s say a print book, may include multiple items that you have generated in different programs (such as InDesign, Photoshop, Illustrator, etc.) prior to placing them in the art file. This can result in different amounts of dot gain in different portions of a page spread.
What Increases or Decreases Dot Gain?
First of all, according to my research, dot gain will be reflected in the series of printer’s marks on your press sheet outside the live matter art. This notation, showing the growth of the dots, may be further broken down into highlights, quarter tones, halftones, etc. So your printer is already actively looking for this problem and seeking to remedy it.
That said, there are certain elements of commercial printing that will make this problem better or worse. According to Getting It Printed:
- Uncoated paper results in more dot gain than coated paper. This is because the ink seeps into the paper fibers and causes the dots to grow. In a similar vein, calendered paper (run between metal rollers during the paper-making process) experiences less dot gain than uncalendered paper. This is because the metal calender rollers create a harder paper surface, and a harder surface allows for less ink absorption into the paper fibers.
- Different printing technologies, such as offset, flexography, gravure, and screen printing, have different amounts of dot gain.
- Different screening algorithms yield different amounts of dot gain. For instance, FM or stochastic screening uses very tiny halftone dots, with more dots in a dark area and fewer dots in a light area. In contrast, AM or traditional screening uses a specified number of dots per square inch, and they are either larger or smaller depending on the percentage of the screen. So these different sized dots will have different amounts of dot gain.
- Higher halftone screen rulings (maybe up to 200 lines-per-inch for coated paper but only 85 lines-per-inch for newsprint) will produce more dot gain since smaller dots grow more than larger dots.
- Different kinds of offset presses cause different amounts of dot gain. For instance, a web offset press is likely to have more dot gain than a sheetfed offset press.
- Inks make a difference. For instance, soy inks produce less dot gain than petroleum-based inks.
- Chemistry makes a difference. Waterless offset printing, which uses silicone-coated plates and no water solution, minimizes dot gain when compared to traditional offset commercial printing.
What Does This Mean to You?
There are prepress applications that deal with dot gain, but since you may have problems in one area of a page and not in another, and since you are probably inserting other kinds of files into your page layout files, my personal recommendation is the following:
- Assume the printer is checking the dot gain charts on the press sheets (printers marks outside of the live-matter page) and adjusting for the dot gain (even if that means burning new printing plates).
- If the quality needs to be above “basic” or “good” (i.e., “showcase” or “premium”), consider attending a press inspection at your printer’s plant, where you can see the press sheets during the press run and make comments and request changes. Let your commercial printing supplier know your plans at the time of the request for quote, however, since a press inspection slows down the overall process (and ostensibly gets factored into a higher price).
- Make your concerns known to your custom printing vendor and ask for feedback if your job needs to be a premium or showcase printed product.
Personally, I’d avoid trying to compensate for dot gain yourself. There are too many variables, and this is the expertise you’re paying your pressmen to bring to your work.
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