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On Press

For all but the simplest jobs, the designer, production manager and sometimes the client will conduct a press check. If one knows what to look for on press, most problems that arise should be correctable. This section will teach how to read the color bars on a press sheet as well as familiarize some common problems that may occur on press and the importance of the final sign-off

Press Sheet

Bars are used to check smoothness of gradation for each of the process colors. Each process color is shown as a solid and as screens, usually 100%, 75%, 50% and 25%. The printer uses these to check dot gain. Patterned boxes, called slur targets, are used to check for ink slurring and movement of the blanket, sheet or plate. Lines show series of resolutions from 3600 to 200. The printer uses these to check resolution ability of film, proof, plate and press. Squares are used to check gray balance in various tonal ranges. The process colors are printed over one another to check solid traps. Magenta, cyan and yellow are combined. If the color balance is correct, a neutral gray is creat

Three Keys to a Good Press Check

Communication - Don’t be afraid to ask questions and talk with the printer. Be prepared to discuss opinions on how the work looks. It is better to raise concerns early than to be dissatisfied with the final result.
Flexibility - Because printers often run 24 hours a day, be ready for the possibility that a press check can be held at any time. Some projects may require several checks. Working overnight is sometimes necessary.
Readiness - Be prepared when looking at the press check. When going to the printer, always bring the original work as well as the latest proof to compare with the press check. Wear neutral colored clothing. Light reflected off colored clothing can alter the appearance of color on the print piece. A loupe should be brought to check halftone dots in the event the printer does not provide one.

Possible Problems when On Press

There are a number of problems that might occur during a press check. Modern print technology has limited or virtually eliminated many of them. Ghosting and Trapping are two of the more common issues that still might be discovered during a press check.

Ghosting
In printing, ghosts are unwanted images that form due to the print process. Ghosts can be either mechanical or chemical in origin. Problems with the press, blanket, or plate can cause mechanical ghosting. Even poor layouts may cause mechanical ghosting. These errors are relatively easy to correct. Ghosts that are chemical in origin are more difficult to diagnose. These ghosts are due to the drying process of inks and how they interact with paper and other inks. Correcting chemical ghosting often requires a great deal of troubleshooting.

Trapping
Sometimes inks may produce the wrong color or appear splotchy. The cause may be poor wet ink trapping. Trapping is the ability of a film of wet ink to stick to another film that is printed over it. Because colors are often printed in combination, their ability to stick together is crucial for even and proper color. Fixing poor trapping usually requires an analysis of the tackiness of inks, absorption rates of paper, as well as drying time used.

Here are some other less frequent problems that may occur during press checks:

Crossovers - Also known as bridge, gutter jump and gutter bleed, crossovers are images or graphics that extend across two facing pages, crossing over the gutter or binding. To check alignment, color match and back-up, just fold the press sheet.
Dot gain - Dot gain is the tendency for the dots of halftones and four-color images to print larger than they are on the film or plate. Printers adjust for dot compensation based on the type of paper selected to make sure images don’t look distorted.
Hickeys - Hickeys are stray spots of ink or irregularities in ink coverage on a printed sheet that appear as small white circles with ink in the center. Hickeys are usually caused by paper or pressroom dust, dirt or picking of the printing blanket.
Holdout - Holdout refers to a paper’s ability to hold ink on the surface consistently so that it will dry in a sharper, more clearly defined dot and produce higher ink gloss. When ink is absorbed into a sheet, it spreads—creating a phenomenon referred to as “dot gain.” Higher holdout means a sharper dot and increased ink gloss, but can also cause ink to rub off or mark the next sheet.
Mottle - Mottling occurs when a paper stock and ink are incompatible, or when there is too much water on the blanket. The effect is an irregular, blotchy application of ink resulting in a spotty or uneven finish and that exhibits high and low spots, or glossy and dull areas on the printed sheet—mostly in solid areas.
Off-set - Off-set, or set-off, is the undesirable transfer of ink from one freshly printed sheet to the back of the next and is usually caused by too much ink being applied to the substrate and/or ink that is slow drying.
Paper dust - Paper dust, also known as linting, is caused by any one of several sources—dust on paper left by dull cutting blades at the paper mills, a printer’s failure to back trim, contaminating flecks of dried ink, the use of too much offset powder or dust from the plant environment. Loose flecks of fiber, filler and/or coating can stick to the printing blanket and prevent ink from properly reaching the paper surface.
Piling - When a press is running too much ink it causes buildup on the press rollers, plate or blanket and makes printing hard to control. Piling also refers to the accumulation of dust or coating on the blanket of an offset press. Piling affects how ink lays on a paper, overall color evenness and can also lead to set-off.
Pinholes - Pinholes occur when ink fails to cover a substrate surface completely, leaving small holes or imperfections in the printed area. This condition is often caused by the presence of foreign matter on the paper or other substrate surface during manufacture.
Unevenness of color - To ensure that ink is laying consistently and evenly, check the color bars across the sheet from end-to-end.
Scumming - Scumming occurs when ink starts to appear on the non-image areas of a press plate. This condition arises for a variety of reasons, basically due to spots or areas not remaining desensitized and will most likely require that plates be changed.
Slurring - Slurring is the smearing or elongation of halftone dots or type and line images at their trailing edges and is usually caused by running too much ink. Check portions of the color bar, which will indicate if slurring is occurring.
Turn-ten - Before running a job, a pressman should take at least ten sheets and run both sides to see how the ink lays on each side. This is known as the turn-ten rule. This step can help address any printing issues before running the entire job.

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