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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 methods used by ceramic printers to remap color from a standard color space into ceramic color space are varied and generally quite proprietary. Unlike conventional offset printing, which typically uses industry-accepted standards and methods for color separation, most ceramic screen printers develop their own color-separation systems. These systems are a combination of prepress techniques and screenmaking, ink, and printing parameters designed to support each facility's unique environment.

Generally, it is not possible to use one set of unmodified films or digital separation files to support printing at multiple facilities. Rather, once the artwork or electronic file is received, each facility must develop its own process-color separation method to reflect the capabilities and limitations of the ceramic inks and production techniques it uses.

Today, almost all ceramic process-color separations are done on a computer. While some facilities use Adobe Photoshop to manipulate color, a few color-separation systems specifically for glass and ceramic decorating are also available.

Regardless of the software used, all separation approaches start with a file created in a known color space, which is then translated into ceramic color. The known color space could be a graphics-arts standard, such as SWOP-CMYK, RGB, or a similar color model. The best color space to begin with varies from facility to facility, so when preparing artwork for a project, make sure it complies with your printer's preferences.

Converting color between a standard space and a ceramic space can be quite time consuming. You can make the conversion manually by "borrowing" color from channels in a standard space to create a new ceramic color channel. For example, a cadmium red ceramic channel might be built from color borrowed from the magenta and yellow channels of a standard CMYK separation. Alternately, you can make the conversion automatically by simply changing the color "mode" or model of the graphic from a standard space, such as RGB, to a predefined ceramic color space. Both of these approaches have their merits and faults.


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