The widely-spread 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 inefficient 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, spot varnish, 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.
Computer Methods of Generating Spot Colors
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, 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.
Optimizing Spot Color Usage
Generally the cost and potential for problems for a print job increase as you add more spot colors, due to the increased cost and complexity of added process inks and films, and requiring more runs per finished print. However, spot colors can be a very powerful weapon in security printing, like money, passports, bonds, and other similar prints that should be hard to forge. Money printing for example, uses secret formulae of spot colors, some of which can be seen by the naked eye, and some cannot be seen unless by using special lights, or by applying certain chemicals.
Digitization of Spot Colors
Spot colors are now a great business for a company like Pantone. The modern trend in spot color matching systems is the digitization of spot colors. This idea came from the fact that a spot color print won\’t be a match to the monitor\’s colors, due to the inherent differences in printed (ink) colors and monitor (light) colors. To achieve a rather good result of simulating the RGB colors into CMYK colors in offset prints, a proper monitor calibration should be done to realize a good balance between reproduction of gray color on paper and on screen.