My experience has been that ivories, being porous, absorb water and then pop off. I usually use rubbing alcohol (or another solvent) since it dissipates rather quickly. It works wonderful. The only caution I might add is that on pianos where the sharps are NOT plastic, oftentimes the alcohol will lift the stains out from the sharps and then you run the risk of smearing the black on your white keys. Be careful and depress the sharps so that they are out of your way (almost). I take my left hand and raise the front of the white key with my thumb and then depress the sharp with my long fingers thereby getting the sharp out of the way. My right hand is then free to clean the Ivory. Ron Shiflet, RPT Phoenix Chapter
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