1. Ink difference: a. Four-color printing: printing with subtractive three primary colors (yellow, magenta, blue) and black. b. Spot color printing: refers to the use of yellow, magenta, blue and black ink other than four color ink to copy the original color of the printing process. For custom printed tin cans, spot color printing process is often used to print large area background color.   2. Difference of printing effect: a. For dark large-area color blocks, the four-color printing process may need to be superimposed by high-salinity dots of several colors, and the ink layer is too thick and easy to show the reverse rub; The selection of spot color printing process only need to print one color, not easy to show the reverse dirt. Select four-color printing process, some parts of the text may be composed of several colors; The selection of spot color printing process, the corresponding part only prints one color to avoid the possibility of presenting overprinting errors for personalized metal tin cans   3. Differences in printing process: a. Four-color printing Printing colorful pictures through the three subtractive primary colors (yellow, magenta and cyan) and black. It is necessary to separate the colorful pictures of the original manuscript for printing into their own color separators, plus black color separators, proofreading cyan, magenta and yellow inks, and improving the blackness of the printed pictures. These films are used to make four plates for four-color printing. b. Spot color printing, packaging products or the cover of books and magazines are often composed of uniform color blocks of different colors or regular gradient color blocks and text, these color blocks and text can be divided into colors and overprinted with four primary colors, can also be assigned spot ink, and then only a certain spot ink is printed in the same color block.   4. Difference in economic benefits: From the perspective of economic benefits, mainly to see whether the selection of spot color printing process can save the number of overprints. Reducing the number of overprints can save both printing costs and prepress costs of metal tin cans wholesale.