There are many reasons that a gold chain will blacken from surface corrosion called tarnishing, the most common being when lower-carat gold comes into contact with sweat and body sprays such as perfume or hairspray. But your jewelry can also suffer when worn while you cook sulfuric, acidic foods such as onions -- and in all cases the black tarnishing can rub off onto your skin. Fortunately, you needn't toss your gold or tuck away in a box. With a little gentle cleaning you can restore its lovely gleam.
Unfasten your gold chain and hold it from one end so that it dangles downward. Fold a soft chamois cloth in half around the upper part of the chain.
Carefully run the cloth down the chain. Repeat this process until you've removed as much tarnish as possible.
Mix 1 teaspoon of dish soap into 1 cup of cold water. Add three drops of ammonia. Stir the solution with an old soft toothbrush. As an alternative, use commercial jewelry cleaner and follow the manufacturer's instructions.
Lay the chain flat on a clean towel and scrub it gently with the wet toothbrush to remove the rest of the tarnish. Rinse the toothbrush as needed to remove the black tarnish. Dip it in the soapy water again before you resume scrubbing.
Rinse the chain with warm water and lay it flat to dry.