It is natural for copper to tarnish over time depending on many factors like the amount of wear, excessive humidity, and exposure to water, sunlight, sweat, etc. Product may need to be polished every so often in order to maintain a nice shine. Many products can be used like steel wool, polishing pads, lemon and salt, vinegar and salt, and even ketchup. Further instructions can be found on google by typing in "how to polish copper".
