The Difference between Spot Color Printing and Four-Color Printing

Posted on 04-07-2024 by

Four-color printing generally refers to the printing process of reproducing various colors of original manuscripts using yellow, magenta, cyan, and black inks. Spot color printing, on the other hand, refers to the printing process of reproducing the colors of the original manuscript using inks other than the four-color inks mentioned above. Spot color printing is often used in packaging printing to print large areas of background colors.

Scope of Application

Spot Color Printing: The covers of packaging products or books often consist of uniform color blocks or regularly gradient color blocks and text in different colors. These color blocks and texts can be printed using the four primary color inks after separation, or spot inks can be mixed and then only one spot ink is printed in the same color block. Sometimes spot color printing is chosen considering the overall improvement of printing quality and saving on overprinting. Four-color printing: Photos taken in color photography reflecting the rich and colorful changes in nature, color artworks by painters, or other images containing many different colors must be scanned and separated by an electronic color separation machine or a color desktop system, and then reproduced using the four-color printing process due to technical requirements or economic considerations.

Visual Effects Difference

The inks mixed for spot color printing are obtained based on the principle of subtractive color mixing, resulting in lower brightness and higher saturation of colors. Spot color blocks with uniform ink are usually printed on-site with an appropriate increase in ink volume. When the ink layer thickness on the plate is large, the sensitivity of color changes to changes in ink layer thickness decreases, making it easier to achieve uniform and solid printing effects.

Blocks printed using the four-color printing process are composed of various colors with certain proportions of halftone dots. During printing, the thickness of the ink layer must be strictly controlled. Changes in ink layer thickness and printing process conditions can easily cause changes in color intensity and variations in halftone dot expansion, resulting in color changes. Moreover, any change in any of the colors composing the block will lead to changes in the color of the block, increasing the chances of uneven ink distribution. Therefore, it's not easy to achieve uniform ink distribution effects with blocks printed using the four-color printing process, especially if the colors of the block cannot be overprinted in one pass of the multicolor machine. Additionally, due to the difficulty in controlling the color of semi-finished products, color deviations may occur. Furthermore, the result obtained from four-color printing is a comprehensive effect of halftone dot subtractive absorption and additive mixing, resulting in higher brightness but lower saturation of the color blocks. For light-colored blocks, the use of the four-color printing process may result in a lack of thickness and a dull feeling due to the low ink coverage on the paper. Also, due to the angle of halftone dots, the presence of patterns is inevitable.

Application Perspective

From the perspective of product quality, when printing large areas of light-colored uniform blocks, it is common to add a medium lightener to the original ink to mix spot inks for printing on-site. This results in a thicker ink layer, making it easier to achieve uniform and solid colors. If the four-color printing process is used, low screen percentage halftone dots must be used. However, low screen percentage halftone dots are prone to small variations during plate exposure, such as slight defects caused by tiny sand particles or inadequate vacuuming, leading to uneven halftone dots. During printing, excessive water supply on the plate can cause accumulation of paper powder on the plate and rubber blanket, resulting in poor transfer of ink for small halftone dots and thus causing uneven ink distribution and lightening of ink color.

For large areas of dark-colored blocks, the four-color printing process may require superimposing several colors of high screen percentage halftone dots. However, excessive ink layer thickness may result in back dirtying. In contrast, using the spot color printing process only requires printing one color, which reduces the risk of back dirtying. Additionally, some parts of the graphics may be composed of several colors in the four-color printing process, while the corresponding parts in spot color printing are printed with only one color, avoiding the possibility of overprinting errors.

Economic Benefits Perspective

The main consideration is whether adopting spot color printing can save on overprinting. Reducing overprinting not only saves printing costs but also saves prepress production costs.

Feasibility of Simultaneous Use

If a product's image contains both color gradient layers and large areas of background color, the color gradient layer can be printed using four-color printing, while the large background color can be printed using spot color printing. The advantage of this approach is that the color gradient layer can be accurately reproduced by controlling the on-site density, while the background color can achieve a visually uniform and solid effect by appropriately increasing the ink volume. This method is commonly used in the printing production of packaging products and stamps, but the increase in the number of colors also increases the cost of printing plates.