Summarize this article in one sentence.
An ivory scraper is a product designed to remove yellowing and stains on ivory piano keys. You can find this tool online or at piano supply stores. Speak to a professional piano technician before you use this tool to avoid damaging the keys. There is a risk that you will damage the ivory piano keys with the ivory scraper if you use it incorrectly. If you are not sure how to use the tool properly, reach out to a professional. If the keys are really yellow or badly stained, you may want to consider hiring a piano technician for the cleaning. The technician will remove each key and clean them individually with an ivory scraper or a professional cleaner. They will know the best and safest way to remove stains and yellowing on the ivory. Getting a thorough cleaning done on the keys once a year by a trained technician may be a good option, especially if you use the piano often.

Summary:
Use an ivory scraper. Hire a piano technician to clean the keys.