18-karat gold items should always be marked with 750, denoting their 18K composition. The marking may require a jeweler's loupe to see and is placed on an area of the piece that does not touch the body to ensure that it is safe to wear. Gold jewelry, with the exception of 24-karat (pure) gold, typically contains alloys to improve its strength. Those alloys can cause the gold to tarnish over time. 24k gold will not tarnish but is not strong enough to be used for body jewelry. Chemicals such as chlorine, perfume, acidic foods, saltwater, or even oils in your skin can accelerate tarnishing. Tarnish can be easily removed from solid gold pieces using silver polishing cloths or jewelry cleaning solutions.