Ed #5 Enhancing Color

Most of the more-than-four-color work produced today relies on manually created bump plates and custom inks. But while touchplates typically apply additional color to a portion of an image, it’s also possible to apply colors across the entire image—to print in six or more colors.

Adding extra colors—or different tones of the four process colors—to CMYK inks can help capture a wider slice of the spectrum of colors visible to the eye and allow designers to create special effects and match custom colors. Depending on the two additional colors that are chosen, six-color printing can be especially useful in reproducing oranges, greens and purples, which are difficult to create by combining two of the subtractive primaries. Six-color may not be as valuable when it comes to blues, which can be reproduced well using the four process colors. However, even blues could be pumped up by using special, high intensity inks or adding an additional blue to the traditional CMYK inks.

Some printers use a complete six-color process printing system. In 1995, Pantone Inc. introduced Hexachrome® six-color process printing, which uses specially modified versions of CMYK inks along with orange and green. The system promises to reproduce more than 90% of all of the Pantone Matching System colors, almost twice the number that can be captured using conventional four-color process printing.

The Hexachrome system is most widely used by packaging printers, who value its ability to faithfully reproduce a wide variety of the colors without ever having to resort to spot colors or change the inks on the press. Once the press is equipped with Hexachrome inks, the press can print a wide variety of projects, in a wide range of colors, with fewer printing plates, less make-ready and wash-up time and no second passes through the press.

People familiar with the system say it can offer other advantages compared to conventional four-color too, including more accurate pastels and outstanding skin tones. Images with dark details and full rich colors, such as dark leather, deep wine, walnut, mahogany and other dark woods may also be good candidates for six-color printing. And high-purity Hexachrome inks are so vivid that that some printers are using them in place of standard process inks to print four-color images with greater opacity and intensity.

But six-color printing is not for every project. Even though the projects can be printed in a single pass through the press, there is still the time and expense of preparing additional plates. The premium inks that often are required are more expensive too. And while six-color process printing can deliver more colors than conventional four-color printing, it cannot duplicate all of the special effects that are possible with two touchplates.

Those are not the biggest drawbacks, however. The greatest hurdle to six-color printing is the need for specialized separating and proofing systems and techniques.

Because six-color printing has a greater range of color than conventional CMYK printing, six-color images must be prepared using color monitors and the additive primary colors.

Any object that radiates light (as opposed to reflecting light, like paper) emits light in the three additive primaries of red(R), green(G), and blue(B). By mixing, or adding, any of these two colors,—in overlapping beams of light on a conventional video screen, for example—the intermediate colors are reproduced. White is formed by combining all three additive primaries, while black is their total absence.

The RGB color space is much larger than the CMYK color space—it contains more colors. But almost all images created, stored or processed using RGB colors must be converted into CMYK inks in order to be printed on paper. And that’s where the trouble begins. The translation from RGB to CMYK is never perfect. Not all of the colors seen on the monitor can be printed, and not all printed colors can be accurately matched on a monitor. So what you see on the monitor is likely to be different than what you see on the proof, or on the press.