Ed #9 > text

Making Ink

Today, the basic ingredients of printing ink, as well as the dry toners used in digital printing (see Ed #8), are the same as they were in Gutenberg’s time.

All inks contain colorants—liquid dyes or dry pigments—a vehicle and additives. Dyes and pigments give the ink its color. Vehicles, which can include petroleum or vegetable oils, solvents, or water, carry the pigment. Additives provide the desired performance characteristics. Driers, for example, help the ink dry more quickly. Waxes help the printed surface resist scuffing and reduce setoff, or the transfer of the image from the front of one sheet to the back of another. Other additives allow the pigments to cover more area, protect against drying too quickly, and improve the way the ink bonds with the paper or other substrate.

In virtually all commercial color printing, ink “works” by acting as a filter, similar to a sheet of colored cellophane. Light passes through transparent inks of the three subtractive primary colors—cyan (C), magenta (M) and yellow (Y)— strikes the white paper and is then reflected back to the eye through the colored ink film. Black (identified by the letter K), is added to enhance the depth and extend the tonal range of the colors.

Intermediate colors—colors other than the three subtractive primaries—are formed by laying one film of transparent ink over another. Any white you see is usually not ink, but paper. While there is an opaque white ink, it often requires multiple applications to achieve adequate coverage, so an opaque white foil is sometimes used instead.

Combined in various percentages, CMYK inks can reproduce thousands of hues, but as Ed #5 noted, four-color printing is not full-color printing. It can only reproduce a fraction of the colors that can be distinguished by the human eye. Oranges, greens and purples, intense shades of any color, and metallic tones can be especially difficult to capture using the four process colors.

To correct this drawback, when matching critical colors, the four process colors are sometimes complemented by spot colors, which are applied as a solid and not made from several overlapping screens. In other cases, touchplates print a second hit, or apply an additional screened color, to an image or a portion of an image to increase brightness or reproduce a color that is hard to capture using only four conventional process inks.