Analysis of Special Colors in Directory Design and Printing

What is meant by four-color offset printing for the table of contents?
The four-color printing process generally refers to various printing techniques that use the three primary colors of yellow, magenta, cyan, and black to reproduce the colors of a color original.
2. What is spot color printing for the cover?
Spot color printing refers to a printing process that uses additional color inks besides the four primary colors (yellow, magenta, cyan, and black) to reproduce the colors of the original document. In packaging printing, the spot color printing process is often used to print large areas of background colors.
3. Which products must be printed using the four-color printing process?
The photos that capture the rich and diverse color changes in nature through color photography, the colorful artworks of painters, or other images containing numerous different colors, must undergo color separation through an electronic color separator or a color desktop system scanning process. Then, they are reproduced using the four-color printing technique. This is done for technical requirements or for economic considerations.
4. What kinds of products would use spot color printing?
The covers of packaged products or catalogues are usually composed of uniform color blocks of different colors or regular gradient color blocks along with text. These color blocks and text can be printed using four-color ink sets after being separated into colors, or special color inks can be mixed, and then only a certain type of special color ink is printed at the same color block. Considering the improvement of printing quality and saving the number of printing runs, sometimes special color printing is selected.
5. How do the visual effects of the color blocks in spot color printing and those produced by four-color overprinting differ?
The inks used in spot color printing are obtained by mixing according to the subtractive color mixing principle. Their color brightness is relatively low and saturation is relatively high. Uniform spot color blocks are usually printed in solid areas and the ink volume should be appropriately increased. When the ink layer thickness on the printing plate is large, the sensitivity of the ink layer thickness change to color variation will decrease, making it easier to achieve uniform and thick printing effects.
The color blocks printed by the four-color printing process are composed of various colors, most of which are formed by certain proportions of printing dots. During the printing process, the thickness of the ink layer must be strictly controlled. Changes in ink layer thickness and variations in printing process conditions can easily cause changes in color intensity. Changes in the expansion degree of the dots, thereby leading to color changes. Moreover, any change in any of the colors that make up the color block will cause the color block to change, resulting in an increase in the chance of ink color unevenness. Therefore, the color blocks printed by the four-color printing process are not easy to achieve uniform ink color. If the color of this color block cannot be printed in one pass using a multi-color machine, it is also prone to color deviation due to the difficulty in controlling the color of the semi-finished product. In addition, the four-color printing achieves the combined effect of subtractive color absorption and additive color mixing of the dots. The color blocks have a high brightness and low saturation. For light-colored color blocks, due to the low coverage of the ink on the paper, the ink color is flat and lacks a thick and solid feeling. Due to the angle of the dots, it is also inevitable that people will feel the presence of patterns.
6. From the perspective of improving product quality, which types of products are suitable for using spot color printing?
When printing large areas of uniform light-colored color blocks, it is usually done by adding a medium-lightening agent to the base ink to prepare the spot color ink, and then conducting solid-color printing. This way, the ink layer is thicker, and it is easier to achieve a uniform and thick effect in terms of color. If using the four-color printing process, low-gain offset screens must be used. However, low-gain offset screens are prone to slightly deteriorated ink distribution due to tiny sand particles or poor air extraction during plate making, causing individual ink dots to become smaller, resulting in uneven color: during printing, it is also prone to excessive water supply on the plate surface. Paper powder accumulates on the printing plate and rubber blanket, and the smoothness of the paper is low, which leads to poor transfer of small ink dots. Thus, the color becomes lighter and the color is uneven.
For large areas of dark color blocks, the four-color printing process is adopted, which may be composed of multiple high-density dots of several colors. If the ink layer is too thick, it is prone to back staining. However, using the spot color printing process, only one color needs to be printed, and there is less likelihood of back staining. With the four-color printing process, certain parts of the graphics and text may be composed of several colors; while with the spot color printing process, the corresponding parts are printed with only one color, avoiding the possibility of registration errors.
7. From the perspective of economic benefits, which types of products are suitable for monochrome printing?
From the perspective of economic benefits, the key factor is whether the use of spot color printing technology can reduce the number of color separations. Because reducing the number of color separations not only saves printing costs but also saves the expenses for pre-press production.
8. Can a product use both four-color printing and spot color printing at the same time?
If a product's image contains both color layers and large areas of solid color, the color layer part can be printed using four-color printing, while the large area of solid color can be printed using spot color printing. The advantage of this approach is that the color layer part can achieve correct image reproduction by controlling the density of the solid areas, and the solid color part can obtain a visually uniform and thick ink effect by appropriately increasing the ink volume. This method is often used in the printing production of high-end packaging products and stamps, but due to the increase in the number of colors, it also leads to an increase in the cost of plate making for printing.
9. When using the four-color printing process, if there is a large area of black solid color, how should the plate-making be carried out to make the black solid color thicker?
When using the four-color printing process, in order to ensure the accurate reproduction of tones and colors, the thickness of each color's ink layer must be strictly controlled. Usually, in four-color printing, the solid density of black should not exceed 1.8. Printing a large area of black solid at such a density will lack a thick visual effect. The commonly used method is to overlap about 40% cyan on the large area of black solid.
A small amount of cyan is overlaid on the black base. From the hue perspective, it still appears as black, but the visual effect will be much more substantial. When only one color of black is printed on a white sheet of paper, during the printing process, paper fibers and paper dust accumulate on the rubber blanket, or for other reasons, it affects the transfer of the ink, which may cause white sand holes to appear on the black solid area. The black and white contrast is very obvious. If cyan screen printing is overlaid, even if there are a few sand holes on the black solid area, since the exposed part is no longer the white paper base but the cyan dots, compared to the black and white contrast, the black-cyan contrast is not as prominent. This can make the black background look more uniform and beautiful.