Flat or Spot Color

A spot color is a special premixed ink that is used instead of, or in addition to, CMYK process inks, and that requires its own printing plate on a printing press. Use spot color when few colors are specified and color accuracy is critical. Spot color inks can accurately reproduce colors that are outside the gamut of process colors. However, the exact appearance of the printed spot color is determined by combination of the ink as mixed by the commercial printer and the paper it's printed on, so it isn't affected by color values you specify or by color management. When you specify spot color values, you're describing the simulated appearance of the color for your monitor and composite printer only (subject to the gamut limitations of those devices).

For best results in printed documents, specify a spot color from a color-matching system supported by your commercial printer. Several color-matching system libraries are included with Illustrator. You can use Pantone Matching System (PMS) It has upwards of 1,000 spot colors. Choosing colors from the Pantone chart allows the printer to exactly duplicate a particular color choice.

Minimize the number of spot colors you use. Each spot color you create will generate an additional spot color printing plate for a printing press, increasing your printing costs. If you think you might require more than four colors, consider printing your document using process colors.

Screen Printing

Formally known as silkscreen, this method employs a porous screen of fine silk, nylon, or stainless steel mounted on a frame. A stencil is produced either manually or photomechanically, in which the non-printing areas are protected by the stencil. Printing is on paper or another substrate under the screen by applying ink with a paint-like consistency, spreading and forcing it through the fine mesh openings with a rubber squeegee.

The production rate, formerly limited by the drying time of the ink has been greatly increased through the development of automatic presses, improved dryers, and UV inks. Rotary screen presses speed up production considerably because they allow for continuous operation. Screen printing can usually be recognized by the thick layer of ink and sometimes by the texture of the screen on the printing.

Versatility is the advantage of screen printing. Any surface can be printed (wood, glass, metal, fabric, cork, etc.) in any shape or design, any thickness and any size. In advertising, screen printing is used for banners, decals, posters, billboards, counter displays, menu covers, etc.

There are many methods of making screens for screen printing. The screen is a porous material and the printed image is produced by blocking holes or pores of the screen representing the non-printing areas. Early screens were made manually by painting the image on the silk-screen mounted on a wooden frame. Masking materials were used to block out unwanted areas. Today, both hand-cut stencils and photomechanical means are used. In the photomechanical method, the screen is coated with a light-sensitive emulsion, exposed to a halftone positive film placed in contact with the screen, and the coating in the unexposed areas is developed to form the image through which the ink is forced on to the substrate using a squeegee. The exposed areas form a hardened stencil, which prevents ink penetration in these areas.

Andy Warhol, the U.S. 20th Century “pop” artist, integrated silkscreen process as a primary part of his painting process. Using the screen print process allowed Warhol to use photo-based imagery in his paintings, screened onto canvas as one of the final layers of each painting. He also produced many portfolios of screen prints with color variations of the same images. Silkscreen inks provided Warhol with a commercial type of color palette that freed him from historical color constraints.