A dirty diamond is one of two things: a rough diamond, or a diamond that hasn't been cleaned in a while. Rough diamonds are uncut & unpolished - hence, they are dirty. But that type of dirty diamond will soon be cut and polished and sitting in a beautiful jewel box in a display case. Then someone will acquire it, and before long, it will become a dirty diamond once again.
Diamonds become dirty. When you wash your hands with a diamond ring on, soap scum clings to it. When you put on hand lotion, it gets grease on it. Shower with your diamond earrings or necklace, and again, you get soap scum. In one short day, your brand new diamond could be dirty!
Acquire an ultrasonic jewelry cleaner the same day that you purchase your diamond jewelry, and use it every single day, without fail. The clarity of the diamond changes when the diamond is dirty - it loses its sparkle. By taking one minute each day to clean your diamond jewelry, you can avoid this, and your diamonds will never be dirty!