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The Top Five Mistakes in Separations

(August 2009) posted on Mon Aug 10, 2009

The most common color-separation problems often have very simple solutions. Read on to find out how you can overcome the issues you commonly face.


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2: Trapping issues or the underbase showing on dark shirts This is one of the biggest headaches in screen-printing separation. Trapping is required in almost all dark-garment printing when the top color completely covers the underbase. The white underprint needs to be skinny and the top color needs to have a slight overlap to prevent the white from showing. Showing underbase really makes the design look sloppy and poorly printed (Figure 4). The production department typically isn’t at fault when this happens; instead, it just means that the art department didn’t take into consideration that the white would spread a little and the top color would need some room to account for this phenomenon and any variation in registration. Trapping can also be an issue with lighter shirts—without an underbase—when the press is shaky or the screen frames are loose. You’ll see the printed images distort as you lay down each color.

Solution: Running tests of images to see how much of a trap is needed in different situations and with different shirt colors will take care of the problem. Carefully document these issues as they come up so that the next time a similar job comes through, the art department will have a standard by which they can create a proper trap on the image. The maddening part is that some images do not need a trap on some garments—say, on a heather-gray shirt—but require one when printed on a different shirt color. A lack of trap may be much more obvious on a white shirt. In these cases, establishing a trap standard takes care of the problem and prepares you for any issues down the road.

I have not found a simple step to selectively trap areas in vector-file-based images. Trapping the underbase typically involves creating an extra file and then adding a white outline to it in the amount of a trap. CorelDRAW and Illustrator have trapping in the software, but the programs don’t allow for selectively trapping just the necessary areas. The ability to selectively trap is a real need in screen printing, because it allows us to prevent certain inside areas of color from mashing together and ensure that outside areas still cover the underbase.


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