Offset printing inks – Basic(III)

- May 18, 2018-

Visual Properties

Visual properties of inks are a function of the colorant or pigment, in relation to the vehicle system used. They include color, transparency or opacity, and gloss. By far, the most widely used ink color is black. Then come cyan, magenta and yellow which are used in process printing to create the millions of colors so familiar to us in printed matter. While the physics of color is a highly sophisticated science, in simplest terms color comes from reflected light. White light contains the entire rainbow of colors. When that light passes through a filter or is separated by a prism or raindrop we see the individual colors in the light spectrum. An ink film acts as a filter on the light reflected from the printed surface, e.g., a red ink film allows the red segment of the reflected spectrum to pass through while blocking the rest of the colors. Because printed surfaces vary in color and in reflectance, they, too, will affect the reflected color. Thus, various ink colors printed individually or “trapped” one on top of the other create different filter effects resulting in different visible colors. Similarly, these same ink colors printed on different substrates will result in visible colors that are different yet.


offset inks on press

When we refer to ink color, we are most often speaking of hue or shade—whether the ink is red or blue or green or purple. Secondarily, we might describe its strength or saturation, also termed chroma. Thirdly, we might indicate how light or dark it is—a reference to its purity or value. The amount of pigment used affects an ink’s color strength, and the type of vehicle used can affect both the hue and the value of the ink color. The color of the vehicle itself, its ability to wet the pigment articles, and even the chemical interaction between the vehicle and pigment can affect the shade or purity. Finally the color of the substrate, and its drying/absorption properties affect the printed color results.

Ink opacity- ability to hide the color beneath it. Sometimes, an ink with little opacity is needed, such as when overlapping two colors to create a third color. Other times, very opaque ink is needed to completely cover any color under it. The opacity must be suited in the use of the ink. Opacity is tested by spreading a sample of ink with an ink knife over a wide black line printed on a sheet of paper. The amount of covering is then compared to a standard to determine if the opacity is correct.

Ink transparency- refers to the opposite of opaque. A transparent ink does not hide the color beneath it, but mixes with it to create a third color. All inks used to print full color work must be transparent. The choice of colorant and the degree to which it is dispersed through the vehicle are the most important factors in determining the transparency or opacity of an ink.

Gloss – refers to an ink’s own ability to reflect light, and depends upon the lay or smoothness of the ink film on the substrate surface. Generally, the higher the ratio of vehicle to colorant, the smoother the lay, and the higher the gloss. Application of a thicker ink film tends to improve gloss while penetration into the substrate tends to reduce.