I was talking clean and shiny but I do know what you mean by polished and tarnished. all in the same, everyone's input was good and valued.
clean is just that. Dirt and grit which can harm your dies is removed from the case but brass can still have a layer of oxidized brass which is a brownish film. Polish is removing the oxidation layer.
Dry tumbling with lizard litter etc removes the oxidation through the friction of the walnut shell media against the case along with the addition of a polishing compound, with the wet methods a mild acid such as vinegar, lemon juice, or a citric acid based cleaner removes it chemically.