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Sprinkle baking soda over the stain. Scrub the stain. Rinse the sink. Dry the sink.

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Use enough to lightly cover the stains. How much or how little you use depends on the extent of the staining. You don't have to do any measuring. Let the baking soda sit for up to 30 seconds. Use a clean soft cloth. Move in circular gentle strokes until you feel the limescale begin to loosen. Keep your strokes with the grain of the surface. Alternatively, you could make a paste by adding a few drops of water to the baking soda. Use the same gentle circular motions to loosen the limescale. Run lukewarm water over the surface. If you have a sprayer, use it to rinse the sink. Otherwise, direct the stream of water over the surface with your hands or a cup. Keep rinsing until all traces of baking soda and limescale are gone. Use a clean cloth or towel with a soft texture. Move in gentle circular strokes with the grain. Continue until the surface of the sink is completely dry. If you leave any water deposits, the lime or calcium in your water will contribute to new buildup.