Brass is a living material and will naturally develop a darker color due to oxidation. Exposure to moisture or grease can reinforce the oxidation and may leave stains and fingerprints. The oxide layer protects the metal and forms a beautiful patina over time but can easily be cleaned off to restore the original brightness and shine. Wash solid brass objects in hot soapy water to clean off grease or wax, and gently rub it with a soft cloth. Use a non-abrasive polish to remove tarnishing and re-shine the surface. Avoid using steel wool or other materials that can scratch the metal.