The black stuff often found on a jewelry cloth is tarnish or oxidation that has been transferred from the jewelry pieces onto the fabric surface over time. Tarnish is a natural process that occurs when certain metals, like sterling silver or copper, react with moisture in the air and other substances present in their environment. This chemical reaction creates a dark coating on the metal surface, which is what appears as black residue on the jewelry cloth when rubbed against tarnished pieces. The purpose of a jewelry cloth is precisely to remove this tarnish and restore shine to your jewelry items by rubbing them gently with its special fibers.