Coudray discusses the influences that ink values, software, and other variables have on the creation of effective simulated-process separations.
The object of simulated process is to choose ink colors that are transparent enough to optically and physically blend but opaque enough to eliminate the need for critical pressure and platen-height controls. Therein lies the basic problem you must address at the color-separation stage and on press.
The natural optical characteristics of each pigment is unique. Some are more transparent and some are very opaque in their natural form. The more transparent a color, the better it will mix with other colors. One of the measures of this characteristic is the tinctorial value of the pigment, which refers to the ability of a color to stand up to dilution with white without losing its color strength. The more transparent a color, the lower the tinctorial value. This is very important when choosing our ink colors.
One of the fundamental flaws within the Pantone Matching System is that it doesn’t address the tinctorial aspect of each pigment. As proof, simply look at the book and you’ll see the huge jump in tone value between Reflex Blue and 279 or between 293 and 292. This indicates a very low tinctorial value of the blues. Compare the same tonal separation between 1925 and 1915. In both formulas, 12 parts of trans white were added to four parts of color. It is clear the reds can hold up better to the addition white.
Now we come to the very important part. When two colors are mixed together (physically), the more opaque color—the one with higher tinctorial value—dominates the resulting secondary color. In other words, when you mix red and blue the resulting purple will have a noticeable shift to the red side. Because the Pantone System, as well as Photoshop, ignore this important component, our ability to reproduce accurate secondary colors is left entirely to us. Results are approximate at best unless the separator adjusts for the known translucency of each ink. Likewise, if the separator uses a value that does not match the value of the ink on press, the results will be inaccurate.
Photoshop does allow for a limited approach to the problem. When you create new channels and named as spot colors, you can designate the Solidity value. This is close to an opacity value—it does not display quite right based on how the ink actually prints. Acceptable values here are 25-75%. Best mixing results on press occur when the values are set to 25-35%. Beyond 35% you begin to see domination by the higher value.
To accurately determine a color’s value, simply print a solid, 2-in. patch of the color on black substrate. With your background set to black in Photoshop, fill a spot-color channel with the desired ink color and adjust the Solidity until what you see on the screen matches what you printed. This is not perfect, but you will be closer than if you had made no correction at all. By adjusting the Solidity value, the separator can now make additional channel corrections if necessary. Print order on press is also very important in terms of varying tinctorial value of each ink color. Remember that the more opaque ink dominates the transition. Therefore, you should use the more transparent colors to overprint the more opaque colors.
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