Brass tarnishes over time, but there are a number of steps you can take to keep your product in good condition.
Exposure: Limit exposure to water and moisture.
Wear: Remove jewellery before going to bed or exercising.
Storage: Store in a cloth bag or brown paper envelope with drying beads or anti-tarnish strip.
Metal Cleaner: Using a soft cloth, rub a gentle metal polisher such as Brasso onto the product and buff to shine.
Home Remedy: Squeeze lemon juice into a small bowl and add 1/2 teaspoon or so of bicarbonate. Dip a pastry brush or cotton pad into the lemon juice and brush/rub over tarnished areas. Wipe dry with a clean cloth and buff to shine.
High Shine: For a really high shine follow either of the options above and finish with a polishing cloth.