Traditional Culture Encyclopedia - Traditional festivals - Why is the color above the copper chafing dish different from that below?

Why is the color above the copper chafing dish different from that below?

The color of the copper chafing dish is different from the bottom of the pot, but it is coated with a protective film. According to relevant public information, in order to maintain the metallic luster of the outer surface of copper chafing dish, it is only necessary to wipe it with a soft cloth dipped with a little toothpaste or powder when cleaning after use, and the outer surface of copper chafing dish is sprayed with a protective film.