What's the best order to print the four colors in four-color process? A definitive conclusion has eluded even the most technical screen printers. Read on to discover how scientific experimentation has established a better answer.
As explained in professor Steven Abbott’s book Moiré, Causes and Cures, A Practical Guide for the Screen Printer (available free of charge from MacDer-mid Autotype), moiré depends on three factors. The first is the math, the second is the human eye, the third is amplification of the mathematical effect. Mathematically, 15° moiré is always present. But the human eye accepts it if its amplitude is below a certain level.
What happens when you print a set of M dots on top of a set of Y dots (or vice versa) is that the dot-on-dot effect fades in and out on a regular basis as some dots (say, every third dot) are printed directly on top of a yellow dot (no dot gain), some are printed mostly in the space between yellow dots (no dot gain), and some are printed on the shoulders of yellow dots and give gain. So the dot-on-dot gain rises and falls in a regular manner, giving a more easily visible moiré. If the second color is mostly above midtone, then the larger dots will, on average, spread out fairly regularly so the amplitude diminishes. That’s why the lily print was so important. The M on Y showed up strongly, but Y on M had no moiré. However, on the test strips, the M on Y and Y on M showed equal de-grees of moiré, albeit with different color shifts, be-cause the dot-on-dot effects are the same.
This leads to a simple rule. If you know in advance that the color that is 15° away from Y (some choose M, others choose C) will have significant areas of midtones on top of relatively solid Y (and it seems that Y tends to be more solid than other colors), then make sure you print the Y after that color. If you don’t have such issues, then you can decide your Y print order based on the pure color criteria of the previous section.
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