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Reworking the Rainbow

(March 1999) posted on Mon Dec 13, 1999

Learn about the issues in color control and proofing that printers face when producing ceramic decals with process-color separations.

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By Jere Williams

The borrowing approach offers artists the most latitude in generating the desired ceramic color, but it is a tedious process that requires much time and expertise. The automatic mode change yields initial separations very quickly, but due to the complexity of ceramic color, each separation may require extensive adjustment before the image is ready for press. With either approach, the quality of the final fired color is only as good as the skill of the people who generate the artwork, print the decal, and fire the decorated piece.

When it comes to building ceramic color separations, the primary challenges involve maximizing in-gamut color fidelity and minimizing out-of-gamut compromises. Those colors that are attainable with a given color model, such as a custom ceramic color space, are called "in gamut." While establishing and controlling in-gamut color is challenging, the approach that works for one project can generally be applied to other similar projects, as well.

Colors that cannot be accurately rendered by a given separation set are called "out of gamut." The rosy cheeks example mentioned previously is a good example of out-of-gamut color. Unfortunately, most conventionally printed colors--to which ceramic decorations are often matched--are out of gamut for ceramics. And to make matters worse, the most troublesome colors are those that give the original image much of its perceived depth, detail, and realism. Out-of-gamut color is the most challenging type to handle when producing separations for ceramic decorating because there are no right answers, only com-promises.

Any solution to an out-of-gamut color will involve compromising one or more of the following color characteristics: hue, saturation, or brightness. An example of such a compromise would be a brilliant blue sky.

Assume that the original art presents a scene representing midmorning on a perfectly clear day. Most likely, the color of the sky on such a day would be beyond the gamut of color you could attain by mixing ceramic magenta and cyan. An extra blue separation to boost the color might be helpful, but, for this example, assume that the cost of an additional printing pass is prohibitive. So the only solutions must come from varying the percentages of magenta and cyan you'll use.


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