This overview discusses halftone styles and how to match them to the designs you print.
Index dots often produce a noticeable texture to the print because all of the dots are the same size so when a piece of artwork has a texture like a pencil drawing, painting, or noisy digital image, it is perfect for the grainy look of an index print. Fine artwork that is created by traditional media, like chalk or charcoal, works particularly well (Figure 5). Another feature that makes art work well for index printing is if the image has very small details, such as little faces, logos, or tiny typography, that need to be clear in the final print. Due to the nature of the index dot, where the dots stack next to each other so there are no open holes as in traditional halftones, small details can be maintained better than in other halftone styles.
Limitations of the index dot are related to the process of creating them and can be the major reason that screen printers decide to not use this style. The primary drawback to index or square dots is that to reproduce a blended set of colors extra screens are typically required. It is harder to create a wide color gamut because the dots do not shrink with lower values. The blending has to rely on the solid colors that are represented. A four-color, simulated print with traditional halftones may require up to six or seven colors with an index dot. When considering this, many screen printers won’t even give the square dot a second look because of the added screens and cost of setup.
The unknown advantages of the index dot do dictate a second look, however, as the big benefit to screen printers is that the dots experience very little dot gain and once one dot can be exposed, all of them can be exposed, so it effectively eliminates dot gain. Both of these advantages can make this type of halftone very attractive to shops that have unstable production environments and longer printing runs because the prints will turn out very consistent with lower issues, even though there are a couple extra screens. In effect, the tradeoff can be worth it if the artwork works with the dot style.
New styles of halftones have become popular again and they can provide a refreshing twist to the older standards of traditional and index dots. There are different methods of getting some of the newer alternative halftone styles. Some of the more common ones are line, mezzotint, and pattern halftones (Figure 6). The difference to using an alternative method to produce a halftone is that it can behave strangely on press and occasionally produce unacceptable results.
Art that works well with alternative halftones
In a sense, using an alternative halftone actually creates a new piece of artwork out of a graphic so it is less about the original artwork and more about how the alternative halftone works after it is applied to the final graphic. The exciting thing about this type of halftone is the random discovery or happy accident that can occur when a different style is applied. An old piece of artwork can appear like an etching or vintage ad if a line halftone is used. Other options can be a mezzotint or pattern that is overlaid on top of a photo to produce a wide variety of effects.
It is important for the screen printer to find an effective method of reproducing values using halftone dots. The key to raising the quality of your printing is to stay open to a variety of functional methods while still being able to apply the right process that will work the best with a specific artwork type.
Thomas Trimingham has worked in the screen printing industry for more than 15 years as an artist, art director, industry consultant, and head of R&D for some of the nation’s largest screen printers. He is an award-winning illustrator, designer, and author of more than 45 articles on graphics for screen printing.
He can be reached at firstname.lastname@example.org.
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