Onyx must be sealed when first installed and then re-sealed at regular intervals. It should also be polished on a regular basis. If spills occur, the stone should be cleaned quickly using a particular recipe cleaner. The stone should then be rinsed thoroughly under running water before being soaked in water with a little bleach added for 10 minutes. The stone should then be washed again until no trace of bleach remains. If you don't wash your car regularly, the wax will build up over time. You should bring it in for cleaning about every six months if you want to keep it looking new.