In the printing of a large area of ​​light-colored uniform color blocks, usually added in the original ink: medium light agent to match the spot color ink, and then field printing, so that the ink layer is thicker, easier to get uniform color, thick effect. If you use a four-color printing process, you must use a low number of flat screen dots. However, the low-grade flat screen outlets are liable to be caused by slight sand particles or slightly poor suction resulting in small dots in individual parts during the printing process, resulting in uneven inks: the printed sheets are prone to excessive water supply. Paper powder accumulates on plates and blankets, and paper smoothness is low, which causes poor dot transfer of ink. As a result, the ink becomes lighter and the ink is uneven.
For dark, large-area color patches, a four-color printing process may require superposition of several colors of high-salted dots. The ink layer is too thick to cause back stains. For spot color printing, only one print is required. The color is not easy to appear dirty on the back. With the four-color printing process, some parts of the graphic text may be synthesized by several colors; and using the spot color printing technology, the corresponding parts only print one color, which avoids the possibility of overprinting errors.