In offset printing, a spot color is any color generated by an ink (pure or mixed) that is printed using a single run.
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 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, 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.
- Create a new spot color.
In your page layout application, create a new spot color, naming it whatever you want such as “Varnish” or “Spot Varnish.”
- Make your new spot color any color.
Although the varnish is actually transparent, for display purposes you can make its spot color representation in your digital file just about any color.
- Don't duplicate an already-used spot color.
Choose a color not used elsewhere in your publication. You might want to make it a bright, vivid color just so it stands out clearly on screen.
- Overprint your spot varnish color.
Set the new color to "overprint" to prevent the spot varnish from knocking out any text or other elements under the varnish.
- Place your spot varnish color in layout.
Create frames, boxes, or other page elements and fill with the spot varnish then place them where you want them. If the page element already has color and you want to apply varnish over it, create a duplicate of the element directly on top of the original. Apply the spot varnish color to the duplicate.
- Talk to your printer about spot varnish use.
Always make sure your printer knows that you are using a spot varnish in your publication.
- Don't use a process color swatch for your spot varnish.
Create a spot color not a process color for your spot varnish. In QuarkXPress be sure the Process Separation box is not checked. In Adobe InDesign, choose “Spot” for Color Type (the default is Process).
- Talk to your printer.
Consult your printer for any special requirements or suggestions as to how they would like to receive your digital files that have spot varnish colors specified, as well as recommendations for the type of varnish to use for your publication such as gloss or matte.
- Spot varnish doesn't show on proofs.
You may be working “in the dark” when using spot varnish. Since a proof is not going to show you how the finished effect will look, you won't know til it's all finished whether or not you got the effect you wanted.
- Adding a spot varnish can increase the cost of a job.
Use of a spot varnish adds an extra separation/plate to the printing process so a publication using 4-color process printing now requires 5 plates and a job with 2 spot colors will need a 3rd plate.