This article examines the benefits of color management and uses an actual job to demonstrate how color can be controlled.
We always use a yellow hybrid screen to avoid the green moirÃ© that plagues all screen printers, but we also use HDS for large vignettes and have even begun to create profiles with all HDS dots. When HDS sees that the next pixel in a dot will cause the dots to touch up, it is free of the AM constraint of making traditional dots. Instead, it might make a couple of little worm-like shapes or one worm-like and one circular dot. Tones transition so smoothly that the effect is a smooth vignette.
The green vignette
With traditional halftones, one must choose to generate moirÃ© in either red, green, or blue. There are 90 degrees within which to work, so black, cyan, and magentaâ€”the three darkest colors that create the most objectionable moirÃ©â€”can be kept 30 degrees apart. But where does yellow go? Any two colors closer than 30 degrees will create moirÃ© in certain tones, guaranteed. So in all our separations, we use a hybrid yellow dot that doesn't have an angle.
The hazard in using hybrids to avoid angle-based moirÃ© is that they have strange dot-gain characteristics. Do not attempt to combine hybrid dots with halftones unless you have color management in placeâ€”or at the very least a separate compensation curve. A hybrid yellow is a beautiful thing; it allows you to keep cyan, magenta, and black 30 degrees apart. No more little green tweedy-looking moirÃ©! Using a hybrid or stochastic yellow is no secret, but without color management the yellow out-gains cyan, magenta, and black, and everything turns yellow. The color has been sacrificed to eliminate moirÃ©.
Using color management, a yellow hybrid combined with a cyan, magenta, and black halftone creates beautiful greens. Green is a common color in a lawn and garden section, and we've gone to great lengths to get it right.
Once we had those big vignettes under control, we began printing in earnest. Banners were printed on our M&R Processors, beam labels and signs on the Thieme inline, and other signage on our Inca Eagle flatbed inkjet. Using maximum GCR and a selection of hybrid dots, these jobs were set up in a dozen prints or less and sailed through production. Bill Balbach, our director of promotional programs, hovered over his promotion but found little to do after saying he didn't like the banded vignette from our first print.
Our press operators locked in on the proofs by zeroing their instruments on the call-outs on the proof and then reading the print (Figure 6). We print color bars on all four sides, but color bars are a troubleshooting tool. If an operator has hit the colors in the call-outs, then he has matched the proof in every way that matters. For example, in the image that is almost entirely green and yellow, we don't particularly care whether the solid magenta in the color bar is off-color, because there is no solid magenta in what we're selling to our customer. We won't extend a setup to obtain a meaningless number.
When we first began this journey, it was tough to get all the variables under control. Mike Ruff of ReyHan PGF was called in as a consultant, and his company's Chromatix program has been instrumental in our success. We have yet to achieve Chromatix certificationâ€”Holland & Crosby in Canada beat us to being the firstâ€”but we are headed down that road and would not be where we are today without Reyhan's help.
Consistency in screens, inks, substrates, and technique is key to any sort of screen printing. When you pair this consistency with effective color management, you'll open up your window of operations and make jobs more forgiving of variations and easier to set up. Recognize that the initial improvements come from flipping switches, and always keep your attention on improving techniques and materials. If you stay focused on fundamentals, your newly found capabilities will prevent variables from eroding your quality and productivity.
About the author
Rick Auterson manages quality assurance at Indianapolis, IN-based Pratt Corp. During his 34 years in the printing industry, Auterson has worked in photopolymers, printed circuits, lithography, flexography, and more. He also was a founding partner of Digital Color Systems, a company that manufactured scanning densitometers and color-data-management software. Auterson has been with Pratt since 2001.
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