An article we featured in July about an experiment to determine the best color order for process-color screen printing drew an insightful response from master printer Michel Caza. Learn what he sees as the key factors for getting the most accurate and intense colors out of a four-color inkset.
By Michel Caza
The reason why I always print yellow last (especially with UV inks) is to avoid the cross moiré related to the difference of only 15° between yellow and the other colors. While the moiré is still present even when the yellow is printed last, the feeble gray value of the yellow makes the moiré nearly invisible. Printing yellow last also helps control the quality of an image (Figure 1), particularly if you’re printing each color separately on a single-color press. Whether you want the image to look colder, warmer, lighter, etc., printing the yellow last allows you to more easily achieve the desired effect and obtain a more attractive print (Figure 2).
Of course, much of the impact of the yellow relates to the substrate and its relative absorption of ink, as well as the number of lines in the halftone. The order of the other colors and the ICC profiles used also has an impact. In my shop, we use ICC profiles for 20 different combinations of substrates, inks, and color sequences.
Compensating for gain or loss
The order in which colors are printed has a substantial influence on the dot gain or loss you experience, and each sequence requires its own compensation curves. Dot gain and loss is inevitable simply because of the nature of screen printing and the fact that the dots are reproduced through a fabric and a stencil. By carefully measuring loss and gain, however, you can change the size of the dots so that they reproduce at the desired size to provide the correct tone in the print. Figure 3 shows how compensation was used with the magenta separation (as an example) for one of our test images. This curve is also applied to the other colors (CYK). Note that using the standard linear tone gradient for offset would have resulted in a loss of detail, particularly in the highlights and midtones, shown as a curve deviating above and to the left of the offset gradient. By moving the tones an equal distance to the opposite side of the offset gradient, we were able to balance the gain and get accurate tones across the range as shown in the grayscale at the bottom of Figure 3.
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