Offset Printing Inks-Visual Properties

By far, the most often ink color is black. Then come cyan, magenta and yellow which are usually used in process printing to create the millions of colors so typical to us in printed matter. As the physics of color is a extremely sophisticated science, in most basic conditions color comes from reflected light. White light contains the entire rainbow of colors. When that light moves through a filter or is separated by a prism or raindrop we see the specfic 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 makes it possible for the red segment of the reflected spectrum to pass through while blockading the rest of the colors.Because printed surfaces vary in color and in reflectance, they, too, will affect the reflected color.For that reason, different ink colors printed individually or“trapped” one on top of the other generate 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. When we refer to ink color, we are most often talking about 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 point out how light or dark it is—a reference to its purity or value. The level of pigment used impacts an ink’s color strength, and also the type of vehicle used can affect both the hue and the value of the ink color. The color of the vehicle entirely, its power to wet the pigment articles, and even the chemical interaction between the vehicle and pigment can affect the shade or purity. Last of all the color of the substrate, and its drying/absorption properties impact the printed color results. Ink opacity- ability to hide the color beneath it.Sometimes, an ink who has little opacity is required,for example when overlapping two colors to create a third color. Other times, enormously opaque ink is needed to totally cover any color under it. The opacity needs to be suited in the use of the ink. Opacity is verified by spreading a sample of ink with an ink knife over a wide black line printed on a sheet of paper. The level of covering is then compared with a standard to check out if the opacity is correct. Inktransparency- refers to the reverse of opaque. A transparent ink does not hide the color beneath it, but combines with it to produce a third color. All inks used to print full color work must be transparent. The choice of colorant and the point to which it is spread out through the vehicle are the most important factors in identifying 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. Usually, the higher the ratio of vehicle to colorant, the smoother the lay, and the upper the gloss. Applying a thicker ink film tends to maximize gloss while penetration into the substrate tends to reduce it.