Press Issues
| Although it's a highly developed endeavor, the application of ink to paper on a printing press is still a high-speed, physical process. As such, it's subject to the vagaries of temperature, humidity, and craftsmanship. Factor in cantankerous machinery, and it's amazing anything ever gets printed. While you can't run the press, you can anticipate some common problems and build your files to facilitate printing. RegistrationSince printing inks are applied to paper in succession, not simultaneously, accurate alignment of the printed inks (referred to as registration) is crucial. While a small amount of misregistration can be easily camouflaged within the natural variation of colors in images, it can be a glaring problem in some special cases. This is most apparent when dissimilar color areas meet with no ink in common. In Figure 2.13, the reversed letters of the two-color logo fall apart if it's printed badly out of register. Is it unreasonable to expect the pressman to maintain tight register? Of course not. But keeping such art in very tight register in two dimensions over a large press sheet can be challenging. Even under the best-controlled press conditions, paper is subject to small amounts of stretching due to the physical stress of traveling through the press. Admittedly, the illustration shows a press sheet that is flagrantly out of register, which indicates two important facts: Press conditions are awful, and you need to start looking for a new printing company. However, even under ideal conditions, such art may suffer at least very small shifts, and you should be emotionally prepared. How can you compensate? If you're allowed to do so, print such artwork in shades of a single color. Then, registration isn't an issue (Figure 2.14). Figure 2.13. Even slight misregister in a two-color logo can be fairly ugly. (Here, bad register is exaggerated for dramatic effect.) Figure 2.14. One solution to registration challenges: Print the logo in a single color. If you're designing a logo or other art element, you should keep this issue in mind. If possible, design to minimize the heartbreak of misregistration by ensuring that color areas share at least one common ink; or, better yet, print in a single ink. The two-color, Brand X logo in Figure 2.13 is an extreme example of artwork that suffers when there is poor registration. But since printing is a high-speed mechanical process, it's unrealistic to expect utterly perfect registration, especially across a large press sheet. Even with very tight controls, slight misregistration can occur. TrappingOne symptom of misregistration on press can be unsightly gaps between color areas that don't share a common ink (Figure 2.15). Figure 2.15. Misregistration can cause gaps between color areas that don't have an ink in common. The remedy for this problem is to use trapping, which involves creating a rim of common color between the dissimilar color areas. In Figure 2.16, the C100-M100 trap is greatly exaggerated for illustrative purposes. In practice, trap thickness is usually around 0.003 of an inch and fairly unobtrusive. Trap thickness may vary depending on press conditions and the conventions of the print service provider. Figure 2.16. Trapping between two dissimilar colors (here, greatly enlarged). Here's some great news: It's not your problem. Trapping is an arcane pursuit that's best left to the print service provider, who uses specialized trapping software. Many trapping circumstances can be complex to resolve, such as those involving metallic inks or neighboring gradients. And some trapping decisions depend on the order in which inks will be printed. You kids don't know how good you have it; we had to hand-carve traps, in the snow, barefoot. In trapping, the darker color defines the edge of objects being trapped to each other, and that determines which objects spread (expand), which objects choke (contract), and which objects remain sharp (unchanged). In Figure 2.17, you can see that different approaches to trapping are required for different circumstances. The trap line consists of a combination of the adjacent colors, and it is usually not as obvious as it is in the illustration. There's some exaggeration in Figure 2.17, to call attention to the trap itself. However, sometimes it is desirable to subdue the visible trap line, especially when lighter colors combine to create heavy trap line. In version D, the color in the trap area is reduced from C100-M60 to C50-M30 to make it less noticeable. In version E, trapping is unnecessary because the objects have colors in common, so there's unlikely to be an unsightly gap in printing. Figure 2.17. Depending on the color, a shape may be spread (expanded), choked (shrunk inward), or left sharp (neither spread nor choked). The darkest color defines the edge, so lighter colors are spread into darker colors. Even though trapping is the responsibility of the print service provider, you should keep it in mind as you design. If you feel that trap lines will mar the appearance of your artwork, consider creating artwork with common colors, so that trapping is unnecessary. Also, as you examine proofs, you're usually looking for large errors such as missing elements or incorrect color. But, as you can see, it behooves you to also be mindful of the little things such as traps. Large Ink Coverage AreasMoving from tiny traps to the opposite end of the size spectrum, you'll discover that large color areas present some problems as well. (You're probably starting to wonder, "Is there anything that's easy to print?") Most ink is translucent, not opaque, and its thickness when applied to paper is measured in ten-thousandths of an inch. Consequently, covering a large area with a single spot-color ink can be challenging. Think of painting a wall. It often takes two coats to achieve smooth color coverage. Similarly, one solution is to apply two passes of the ink (called a double hit). But this can increase the cost of the job because it involves an additional unit on the press, as well as extra ink. Depending on the ink color, the first instance of the color might be a screen tint (say, 50 percent) rather than a solid, to avoid an overly heavy final appearance. If the job already uses a four-color process, a less expensive alternative is to create a process equivalent of the screened underlay described in the previous paragraph, then run a single pass of the spot color on top of it. Before you take the law into your own hands and start trying to solve these problems on your own, have a conversation with your print service provider about the issues involved. Don't over-engineer the job in an effort to help. Either seek guidance from the print service provider's prepress department, or leave it to the professionals to handle your job appropriately for their printing conditions. While you may incur some additional cost, these special treatments pay off in a more professional finished piece. Rich BlackYou don't have to be running spot colors to have large color areas requiring special treatment. Solid black areas bigger than, say, one square inch, usually need to be beefed up or they will appear anemic. The solution is referred to as rich black, but the definition of a rich black varies by print service provider. In some cases, just adding a bit of cyan (40 to 60 percent) is considered sufficient, although this can result in a cool black with a bluish tinge. To avoid a color cast to the rich black area, many print service providers add a neutral balance of the three other process colors. This author was raised to believe that C60-M40-Y40-K100 constituted rich black, but your mileage may vary. And your print service provider may fervently disagree with that recipe. As always, consult your print service provider for guidance. If artwork or type knocks out of a rich black area (also called reversing out), it will require special handling to keep edges sharp to avoid an ugly appearance (Figure 2.18). Once again, press misregistration is the culprit. Figure 2.18. Misregistration in a four-color rich black can be ugly. This calls for special handling. Remember that, in trapping, the darkest color defines the edge. The case of rich blacks might be considered a sort of reverse trap. You want only one color to define the edge of the type or other white artwork: the black ink. To accomplish this feat, it's necessary to pull back the other colors so that if there is any misregistration, they don't peek out and create a pink, blue, or yellow halo at the edge of the reversed type. As you can see in Figure 2.19, the white type is knocked out of all four plates of a rich black area. Since the black plate defines the edge of the type, its knockout is sharp (not choked or spread). But the knocked-out type is pulled back in the cyan, magenta, and yellow (hence the bloated appearance). This same approach is used for type or art reversing out of a double-hit spot color. Figure 2.19. Special treatment for text reversed out (knocked out) of a four-color black. Here comes the familiar, comforting reminder. Setting up this pull-back treatment is the print service provider's responsibility. But it's good for you to be aware of these complexities as you design. All this trapping, knocking out, spreading, and choking (sounds kind of violent, doesn't it?) may be part of the daily grind for the print service provider, but if your job requires a lot of special handling, you may incur extra charges and extended deadlines as a result. Be mindful of your print service provider's specifications for minimum type size that can be safely reversed out of a multicolor build such as a rich black. Problem InksInks are a mysterious amalgam of pigment, the vehicle carrying the pigment, solvents, waxes, and extenders. Ink problems can be caused by multiple issues, including inadequate drying time, absorbent stocks, and poor adhesion. But some problems arise from the pigments themselves. Because of its common use and stubborn personality, perhaps the best-known is Reflex Blue, which is roughly a navy blue. Reflex Blue is notorious for scuffing, smearing, and slow drying times. Navy blue seems to be a primal human favorite. Naturally, everyone wants to use lots of itwitness all the flags and logos that use it. If you use Reflex Blue in your job, be prepared to tack on an extra day or so for additional post-press drying time. Additives can speed up the drying process. Depending on how heavily the color is used in your job, you can also expect slight surcharges for protective coatings (discussed later in this chapter). An aqueous coating, applied on press, is a common solution. Clear aqueous coatings usually cover the entire printed area, preventing scuffing without changing the color of the piece. While Reflex Blue is used in formulating many of the dark blue Pantone colors, it's most troublesome by itself. It may also contribute somewhat to slower drying times and scuffing to some extent in inks mixed with it, but not as aggressively as when used alone. Specialty InksMetallic and fluorescent inks can add visual interest to a printed piece. Metallic inks, while somewhat expensive, are still less costly than using foil stamping (a special finishing process involving heat, pressure, and thin sheets of metallic foil. See Chapter Three, "Binding and Finishing," for more information on foil stamping). The problems they pose are once again due to key pigments. Actual aluminum or bronze (zinc/copper) powder provides the basic metallic appearance, while additional pigments introduce other tinges. Metallic inks as accents are not too troublesome but such inks can mottle over large areas. Unlike most inks, metallic inks are almost opaque, which affects trapping and the order in which the ink is printed. Usually, metallic inks are printed first because of their tendency to adhere poorly to previous inks. While metallic ink will never be as shiny as foil stamping, it's most convincing on coated stock and may almost completely lose its metallic appearance on very absorbent uncoated stock. Varnishing metallic ink will not make it shinier (in fact, even gloss varnish will slightly diminish the metallic appearance), although it will subdue metallic ink's tendency to scuff and flake. If you're creating stationery, be very cautious about using metallic inks. The stress of being passed through a laser or inkjet printer can cause metallic flakes to dislodge and find new homes deep inside the printer. Because of the metallic content, the inks are also subject to oxidation (especially the bronzes). While varnishing (discussed on the next page) may slow down the process, be emotionally prepared for some dulling over time. Also be prepared to consider somewhat extended drying times as part of your job timeline. Fluorescent inks can add a vibrant punch, but their pigments have a limited life span, especially if exposed to sunlight for extended periods. Printing a double hit of the ink can enhance its vibrancy, since fluorescent inks tend to be transparent. They are also sensitive to heat, so such inks are not the best choice for stationery that will be run through a laser printer or copier because of the heat involved in fusing. Custom Mixed InksIf you just can't find a Pantone, Toyo, or DIC ink to match the color you want, your print service provider can custom-mix an ink that's just right for your job. Expect to pay more for this service since it involves extra labor and may consume extra ink (mixed as insurance for the print service provider). If you anticipate reprinting the job at a later date, tell the print service provider up front so they can retain the recipe for future use. It's not practical to "mix enough for later." Unlike wine, ink does not improve with age. Coatings and VarnishesCoatings are applied for two reasons: for special visual effects or to protect ink from scuffing or rubbing off. There are three general categories of coatings in print:
Note that since varnishes and aqueous/UV coatings are sealants, it's necessary to apply the varnish or other coating as the last pass. Pieces requiring gluing (such as pocket folders or packaging) require spot application of such coatings, since gluing and folding take place after varnish or other coatings are applied. Spot application applies the varnish much like an ink, isolating it to certain areas (rather than applying it as an overall coat), so that glued areas are free of ink and varnish. This allows the glue to adhere correctly. |
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