China is a vitreous (smooth and glassy) form of baked clay. It is strong but can be chipped or broken easily, especially cup handles.
Most modern china can be washed in the dishwasher. Hand painted, metal trimmed, or antique china may be faded by the hot water and strong dishwasher detergent. Wash that by hand, or, if you have a set, test by washing the same piece daily for several weeks in the dishwasher and compare with the rest of the set to see if there is fading.
Black marks may show up on china or other white dishes, if aluminum utensils, including foil, have rubbed against china in washing. Load dishwasher so aluminum cannot touch china while washing. Remove marks with a plastic scouring pad and a mildly abrasive cleaner. Never use any abrasive powder for any other reason on china; it may remove metallic or other decorations. Remove tea stains from cups with a solution of 2 tablespoons chlorine bleach per quart of water; soak for just a minute or two; rinse promptly. OR use a commercial product.
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The only way i have found to get the gray marks off white china is a cleaner called Chinamate. Its a liquid that you soak the white china in for 3 hours and it completely removes the gray marks from the china without harming the glaze. I wouldn't put any china with designs in it because it might remove them, too. thanks...