Residues of black tea in cups / jugs
If you can not remove stubborn tar residues, you can do the following:
Rinse the dishes once and then fill with 2-5 tablespoons of normal cooking salt depending on the size or degree of soiling (important: the dishes must not be filled with water, so empty them first).
Then brush / brush with a brush or hand on the soiled areas until you realize that the areas are clean.
Rinse briefly after cleaning and the dishes are mirror-smooth again.