Spot color

In offset printing, a spot color is any color generated by an ink (pure or mixed) that is printed using a single run.

The widespread offset-printing process is composed of four spot colors: Cyan, Magenta, Yellow, and Key (black) commonly referred to as CMYK. More advanced processes involve the use of six spot colors (hexachromatic process), which add Orange and Green to the process (termed CMYKOG). The two additional spot colors are added to compensate for the ineffective reproduction of faint tints using CMYK colors only. However, offset technicians around the world use the term spot color to mean any color generated by a non-standard offset ink; such as metallic, fluorescent, or custom hand-mixed inks.

When making a multi-color print with a spot color process, every spot color needs its own lithographic film. All the areas of the same spot color are printed using the same film, hence, using the same lithographic plate. The dot gain, hence the screen angle and line frequency, of a spot color vary according to its intended purpose. Spot lamination and UV coatings are sometimes referred to as 'spot colors', as they share the characteristics of requiring a separate lithographic film and print run.

There are various methods to incorporate rather sophisticated patterns of spot colors in the final prepress artwork. Software applications such as Adobe InDesign, Adobe Illustrator, CorelDRAW, QuarkXPress and Scribus may generate spot colors as additional channels. Adobe Photoshop can also be used to generate soft edges (widely known as feathered edges) of spot colors. The dissolve effect provided by Adobe Photoshop layer patterns can be generated for any spot color.

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Wikipedia