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The Print Sequence Project

(July 2007) posted on Tue Jul 24, 2007

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.


By Tricia Church

click an image below to view slideshow

The most satisfactory method for the three-color tones turned out to be a simple measure of the %K along a 0-100% three-color tone strip followed by adding together the difference between the measured %K and the specified value. Again, the results were put on a 0-100% scale with the average set at 50 and perfection defined as 100%.

Because the shadows are so im-portant for a good print, and because the Caza b sequence showed a clear advantage over the other prints (there is no dot-on-dot gain when the K is printed first) we wanted to do the same sort of measure as with the three-color tones. Unfortunately, our printed four-color strip was a pure theoretical strip with no GCR/UCA. It showed enormous dot gain, making the measurement technique unsatisfactory. We reluctantly resorted to an expert relative assessment of the degree of shadow clarity (using the proof as a reference standard), and to be consistent with the other measures gave the prints a score either side of 50 with a scatter similar to the other measures.

 

15° moiré

Our subjective judgments of the print quality were greatly affected by the fact that prints one, three and seven had terrible moiré visible in the pretty lily. The reason quickly became clear. In each case, we printed a light M tint on top of a relatively solid Y. This isn’t entirely obvious because sequence 3 is YCMK; but the lily has almost no C, so the M was going directly on top of the Y. The next fact to check was the screen angles. The Y and M are indeed 15° apart. You would not expect any moiré from Y and C as they are 45° apart, and there isn’t much K on Y printing. Why were we seeing moiré only in M on Y? The important answer is that we weren’t! In the four image prints, it happened that only the lily was set up to show the moiré. Very strong moiré of both M on Y and Y on M in the middle tones was evident in the two-color test strips.


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