Bronze is a copper based metal that is an alloy of Copper and Tin. It's a beautiful colour. It does tarnish as all copper based metals do. It will slowly darken in colour, but can be cleaned in a tumbler or with a silver cleaner. Vinegar or lemon juice will also clean copper based materials. All copper based metals must be rinsed well and dryed throughly when cleaned. If you put wet rings in a bag they go jet black and can be ruined.