February '13

For the Business of Apparel Decorating

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Index Separations Made Easy Master the square dot in six simple steps by n Intermediate Thomas Trimingham Index color printing uses pixels in the computer to generate random "spots" on film or screen in a square shape. It uses squares because they are easier to generate, however are neither as precise nor as demanding as (AM) halftone patterns. The benefit to index printing is more about processing speed, not print quality. It is similar to simulated process in that the colors are not specific densities of C+M+Y+K, but are selected by the artist to make a killer (but not technically precise) T-shirt. (Definition courtesy Joe Clarke, CPR) T he subject of index dots seems to be polarizing to screen printers; they either love them or hate them. The position they take seems be related to whether the typical artwork they print is that which works best with index dot screen printing. The individual dots in index screen prints tend to look like grains of sand and this helps or hurts artwork depending upon how it is designed in the first place. For example, super smooth, polished artwork doesn't achieve the best results when separated for index printing. Thomas Trimingham has more than 20 years of experience in screen printing as an artist, industry consultant, instructor and head of R&D for high-volume screen printers. He is currently a senior artist for Illinois-based Sportdecals. Find more information on his website at: Printing clean graphics with square dots also relies on precise ink colors. An index dot is an isolated pixel (or square of color). So, to get good results, the color must be solid and a specific. For this reason, printers that do a lot of index color printing tend to be mixing colors often and will typically have quite a few colors to match in an average image. Of course, the upside to this is, once the colors are dialed in and the screens are set up on the press, the print run will usually have very little dot gain due to the fact that each dot has its own area to fall into. (Dot gain is the tendency of the printed halftone dot to change in size when printed, compromising the quality of the print.) Index color separations almost always have more colors than a simulated process design. This is because of the nature of the separations and the way they are averaged into a blend. Most simulated-process designs that have a gradient between two colors can be split into two colors. But in an index design, a gradient of two colors may need an extra color in the middle to look right. These added colors can hurt in screen costs if the print runs are smaller. But, the extra effort stands to pay off if the image is well-suited to a square dot and if it means eliminating dot gain on press. Essential considerations When considering whether to take on index dot separations, first determine whether your ink department can handle it. The ink department must be able to mix colors and 54 | Printwear PW_FEB13.indd 54 February 2013 1/18/13 10:08 AM

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