If you mean the dark ring or circle around a faucet base on a sink, it’s usually caused by mineral deposits, soap residue, grime, mold/mildew, or corrosion.
Try this first
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Clean the area with warm water and dish soap.
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For a stubborn mineral ring, soak a cloth or paper towel in white vinegar, place it around the stain for 10–20 minutes, then scrub gently with a soft toothbrush or non-abrasive sponge.
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Rinse thoroughly and dry the area.
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If there is black mildew around the faucet, use an appropriate bathroom/mildew cleaner according to its label.
Important: Don’t mix vinegar with bleach or other cleaning products. Also avoid abrasive powders or steel wool, particularly on chrome or polished fixtures, because they can scratch the finish.
If the dark circle doesn’t come off at all, it may be damaged/corroded finish or staining underneath the faucet rather than surface dirt. In that case, removing the faucet and cleaning or replacing the gasket may be necessary.
If you can send me a photo of the dark circle, I can tell you what it most likely is and the safest way to remove it.
