If your ivory keys have become stained, have yellowed or have lost their shine it is probably best to hire a professional to clean them but if you are feeling brave, here is a tip that “Johnkie” posted on the UK Piano Page Forum.
Putting the shine back on your keys whether ivory or not is not too difficult. As has already been suggested, you could get your tuner/technician to take your set of keys back to a workshop and have them professionally buffed. That would restore the shine, but not the mirror finish. If they are worn and grainy, they would have to be scraped, papered, and finally buffed (if the ivory is in good enough condition and thickness to start with). However, if you have the time and inclination, you can improve things drastically by using a clean piece of cotton cloth wrapped around your index finger tip that has been dipped in either metal cleaner ( Brasso, meppo ect) or even T-cut (used for taking the bloom off of car paintwork). It’s perfectly safe and will restore the shine. Don’t worry about any that may get onto the black keys, when it dries it will simply wipe away. Just be careful not to catch the ivory under the front “lip” with the cloth, else it might pull the ivory off. The more time and effort you put in the better the result will be. When trying to cleans piano keys, never use anything other than a damp cloth or the above mentioned types of gentle cutting compounds – Milk, lemon, meths, or “aunty Mary’s top tip solution” are NOT how to look after your piano keys. This works with all types, plastic or natural ivory – Ivory just takes more effort being that much harder than plastic. Good luck and happy shining
Johnkie also went on to say
Most customers flinch when I say use Brasso metal cleaner …. The thought of using something that’s marketed to clean metal is initially too much for them to contemplate… but when I tell them that they can buy a bottle of KEYWHITE from a piano shop … which does exactly the same thing, but costs more and and doesn’t work quite as well they tend to then believe that it would be ok. I always advise them that (especially with non-ivory key tops) once they start, they’ll have to carry on doing them all because it makes such a huge difference. T-cut is not quite as easy as metal polish though … it works but unlike Brasso when it dries it take a little more effort to wipe off the surface residue.