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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

While the peak temperature of the kiln is important, it is also important that the pigments themselves reach a particular temperature. With heavy pieces of ware, longer exposure to peak kiln temperatures may be necessary for the ware and pigments to reach the correct temperature. If the ware is not exposed to peak temperature for a sufficient amount of time, the pigments in the decal may not mature, resulting in a decal that is underfired. The color of an underfired decal will tend to be dull and muddy, and the surface finish may lack gloss.

Conversely, if a decal is overfired (exposed to an excessively high temperature), colors may burn out and lose vibrancy. Differences of just 20-30°F (approximately 10-15°C) from the optimal firing temperature recommended by the color supplier can degrade final image quality.

The atmosphere in the kiln can also influence color, especially with cadmium colors. If the kiln provides insufficient air circulation, cadmium colors may fail to develop. Ceramic printers usually print cadmium inks as heavily as possible to minimize this problem, but the heavy pigment load alone won't compensate for a lack of circulation. So it is important to conduct test firings of sample decals in order to identify and resolve problems as early as possible.

Hope on the horizon

While conventional offset printers can rely on a highly repeatable contract proof as a cornerstone around which to build a successful print run, ceramic screen printers have only the final fired result for guidance. And this final result is subject to a long list of variables, such as printed dot size, ink thickness, concentration and mixture of pigments in the ink, and the exact temperature and atmosphere within the kiln during firing. With such a broad range of variables, it is very difficult to yield subtle changes in one area of a print without introducing subtle and unwanted variations into other areas.

Recent technical advances offer hope for resolving some of these issues. As color separation technology and color management through ICC profiling are developed further, it may be possible to get fairly reliable translations into and out of ceramic color. These translations would enable ceramic printers to offer more economical separations, reduce the cost of art development, and make prepress proofs feasible.

Additionally, ceramic pigment manufacturers are continuing to develop the quality of their pigment ranges, which should reduce the amount of out-of-gamut color that printers must resolve in order to yield a color-accurate product. Until these solutions become available, however, printers must continue to rely on their knowledge of ceramic colors and careful control of the entire decorating process.

About the author

Jere Williams is the Prepress Manager at Heinrich Ceramic Decal, Worcester, MA. He has more than a decade of experience in the screen-printing industry, and has been involved in applications such as textile decorating, point-of-purchase graphics, and decal screen printing.


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