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:

1. 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.
2. Different printing technologies, such as offset, flexography, gravure, and screen printing, have different amounts of dot gain.
3. 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.
4. 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.
5. 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.
6. Inks make a difference. For instance, soy inks produce less dot gain than petroleum-based inks.
7. 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:

1. 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).
2. 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).
3. 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.

Photo purchased from … www.depositphotos.com

About two decades ago I was a custom printing consultant helping a client produce periodicals analyzing the actions of Congress in Washington, DC. It was a Friday night, and their flagship publication was on press at a local printer on a heatset web press. A tornado came in at that very moment and tore the roof off the commercial printing plant. When I called the sales rep, he said my client’s company was “on its own.” The job would not be printed and sent off to its paying customers that night.

So I contacted a local sheetfed printer I knew wanted the contract for this weekly magazine very, very badly. When I called the plant manager, who was at a bachelor party at the time, he agreed to be my client’s white knight. I sweetened the pot by noting that his successful completion of this job would probably create a vacuum that would suck all of my client’s jobs out of the web-press plant into his sheetfed custom printing plant.

He coordinated a new transfer of all digital data from my client’s office to his shop and produced the magazine via sheetfed lithography. Paying customers received a magazine that looked far better than prior issues. It came out on time as though nothing had happened. Within a year or so, the new printer was producing all of my client’s magazines.

Sheetfed vs. Web

The prior example might read like a fairy tale, but it’s actually true. That said, it was more expensive to print the magazine via sheetfed offset lithography than heatset-web offset lithography. Here are the differences and the reasons to choose one kind of press or the other for your own commercial printing work.

Both kinds of presses print via offset lithography, in which image areas on a flat custom printing plate are treated to receive ink, while non-image areas are treated to repel ink. When the press is running, ink is transferred from a printing plate to a rubber blanket and from the blanket to the paper (hence the term “offset”). So in this particular way, web presses and sheetfed presses are similar.

That said, paper is fed into a sheetfed press as individual sheets stacked in a pile at the front end of the press (even if they had initially come from a roll and had been cut into sheets). The sheets are pulled through all inking units, where they receive ink from the plates and blankets. Stacks of printed press sheets (printed on one side) exit the press and are stored for the ink to dry (via absorption into the paper and/or oxidation into the air, depending on the paper in use). Then the piles of press sheets are turned over and run through the press again to print the opposite side of the sheet (called “backing up the sheet”). Final printed sheets (printed both sides) are then brought into the finishing department for folding, trimming, and other post-press work.

In contrast, on a web offset press, paper comes from a roll. As the press runs, the ribbon of paper coming off the roll is held in tension as it enters the press. Like a sheetfed press, the web press uses plates and blankets on each inking unit to print the job.

If the paper is uncoated and the quality requirement is low (such as a newspaper or newspaper circular), the web press can be an open web (or non-heatset web). The ink dries through absorption only (ink seeps into the uncoated paper).

If, however, the paper is a coated press sheet (or roll, more accurately), the applied ink (usually four colors for this kind of work) has to be dried differently. So once the ribbon of printing paper from the web roll exits the printing units, it must enter the drying ovens, which flash off the solvent from the printed ink with intense heat (i.e., drying by oxidation rather than absorption), hardening the custom printing ink on the surface of the paper rather than letting it sink into the paper fibers. Then the ribbon of paper (the web) travels between the chill rollers, which bring the paper back to room temperature.

At this print, the web press can actually do some of the finishing work in line, getting the press signatures (in the case of my client’s magazines, for instance) ready for binding (some web presses do some kinds of binding in line as well).

Sheetfed presses can’t do this. (Finishing in this case is done in another department.)

Web presses are lightning fast. My random query on the internet notes that a sheetfed press can print 15,000 impressions per hour, while a web press can print 50,000 impressions per hour. (I don’t know how precise these numbers are, but the gist is that web presses are significantly faster than sheetfed presses.)

Moreover, a web press prints both sides of the roll of paper at one pass, unlike a sheetfed press. Either the ribbon of paper is turned over within the printing process using “turning bars” (with four of the inking units printing one side of the paper and then the other four inking units printing the opposite side), or press rollers, plates, and blankets above and below the web of printing paper print both sides simultaneously. This also speeds up the process dramatically.

But speed has its drawbacks. Even a heatset web press (as opposed to a non-heatset web press, which some people call a coldset web) cannot in most cases match the level of quality produced by highly skilled operators on a sheetfed offset press. (This is why my client’s customers who received the tornado edition of their magazine were knocked off their seats by its quality.)

In contrast, speed does yield cost savings. Sheetfed printing involves separate finishing operations in a different department, and overall it progresses more slowly, so the final bill is usually higher, depending on the total press run.

To illustrate, when I was an art director, my employer printed 60,000 copies of a 384-page (approximately) 6” x 9” perfect-bound print book (twelve 32-page signatures). The text was printed on a web press. I believe the 60,000 covers, since they were small, they could be ganged up on a single press plate, and they had to be of very high quality, were printed on a sheetfed press. I’m not good with math, but it seems to me that at 15,000 impressions per hour vs 50,000 impressions per hour, it would take much, much longer to print twelve 32-page press signatures (twelve separate press runs) on a sheetfed press than on a web offset press.

Why Choose One Press Over Another

If you’re buying printing and deciding what kind of printer to approach for a bid, here are some thoughts:

1. If you’re producing a textbook, for instance, as was part of my job as an art director, consider the number of pages multiplied by the number of copies. In my case of 60,000 copies multiplied by 384 pages, that would be 23,040,000 book pages. In my experience, that’s definitely a web-offset commercial printing job.
2. If you’re printing 60,000 copies of a 8.5” x 11” flyer that will be laid out (imposed) eight-up on a press sheet (eight final copies per 25” x 38” press sheet), then your final print run is actually only a fraction of the total or 7,500 copies, because out of every press sheet you get eight copies. That would most probably be a sheetfed job.
3. Quality. Maybe you wouldn’t print an annual report on even a heatset web press. I wouldn’t. Even if it can run coated paper and four-color process ink work, it probably won’t look quite as dynamic as a sheetfed-printed annual report. However, if you’re producing flyers, forms, brochures, newspapers, newspaper circulars–either a heatset web press (for coated printing paper) or a non-heatset web press (for uncoated printing paper) might be a good bet. The key here is the length of the press run.
4. So back to press runs. If you’re unsure, ask your printer. But my random check on the internet suggests 10,000 to 15,000 copies as a starting point for web offset, for magazines and brochures. While I would definitely agree with their assessment as it pertains to magazines (multiple custom printing press signatures multiplied by 10,000 or 15,000 copies), I think for brochures or any other work that can be ganged up on a press sheet, your target totals for choosing web offset lithography over sheetfed lithography would be much higher.

But it never hurts to ask your printer.