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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 controlling color is challenging in any type of screen printing, printing designs for ceramic and glass decoration poses some unique obstacles. Among the most significant is that the image color at the time of printing is quite different from the fired color, which won't be seen until several hours, or even days, later. In the following pages, I'll take a closer look at this and other issues in color control and proofing that printers face when producing ceramic decals with process-color separations.

Fundamentals of ceramic color

Screen printing for ceramics is generally done in one of two ways: Colors are printed directly onto the ceramic or glassware, or they are printed onto decal release papers and then transferred onto the ware. In either case, after the decoration is applied, the product is fired at temperatures ranging from 950-2200°F (510-1205°C) to yield the final image.

Decorations on ceramic and glassware range from solid, single-color designs to continuous-tone spot-color images featuring upwards of twenty colors, and from basic process-color images to process colors with additional integrated "boost" colors. The final fired design is extremely durable and may include many special effects, such as bright or burnished gold and platinum, iridescent colors, and textures. All the fired colors are permanent.

The color fidelity of a fired decal depends on three major factors:

1. Pigments Ceramic pigments tend to be much less pure and vibrant than the corresponding pigments in conventional printing inks, such as those used for offset lithography and screen printing.

2. Color space Because of pigment limitations in ceramic inks, the color information for the original image must be "remapped" from a standard color space, such as SWOP-CMYK, RGB, or L*a*b, into the unique color space that will be used to render that image with ceramic colors. However, even after a color has been remapped into ceramic color space, significant areas of the conventional-printing color space will remain unattainable.

3.  Firing Fired color is the result of chemical interactions that occur within the inks at high temperatures. Therefore, anything that influences these interactions will affect the final color.


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