Like other metals, nickel will begin to tarnish. In time, the sheen of the nickel will dull and become darker in colour. The tarnishing will continue to darken unless you clean it. This cleaning process will restore any nickel-plated item to its original lustre and shine.
First, mix water and ammonia in equal parts, enough to immerse the object in the mixture. Add the ammonia solution to the bowl or container. Allow it to sit for 30 minutes.
Second, remove the item from the solution. Gently scrub the object with the soft-bristle brush to remove tarnish. Repeat in 30-minute intervals until the tarnish is gone. Rinse and dry the piece completely.