I have a beautiful old upright piano, that as of now, is at least 99 years old. I got it from my parents, who got it from my paternal grandmother, whom I presume bought it new in about 1927 or so. It is a fine old instrument, and I love playing it. Nothing wrong with the action on it. It won’t hold its tuning nowadays, which makes it all the more fun when I play ragtime or similar. Sounds like a honky-tonk piano like you hear in Westerns.
But the white keys are real, genuine ivory, on wooden keys. I remember my mother cleaning them with milk when I was a child, claiming, “Milk cleans ivory.” They looked a little better after a cleaning, but not perfect.
In the twenty-five years that I’ve owned it, I’ve never cleaned the white keys like Mom did. I didn’t see the need; I’m the only one who plays it, and I know where the white keys are, and it still sounds good (to me anyway). The keys are a yellowish-brown, but still identifiable as white keys.
I have no interest in cleaning the ivory keys, but playing my piano recently, I got to wondering, “Does milk really clean ivory?” Hence my question.
I am not an expert, but I assume these folks and these have some idea of what they’re doing.
From the second link:
If your piano keys are real ivory, you are probably aware they were once bone of a living creature. This being the case, they are very naturally porous.
This means that using other natural items like diluted lemon juice, or even milk, can be a good method for cleaning. This is because the naturally occurring acids in things like milk or lemon juice help fight the yellowing stains on cleaning ivory keys.
Of course, be careful to dilute the acids so they do not wear down the bone.
It’s also best to allow each key or set of several keys, to dry thoroughly before moving on to the next.
Boy, I’d worry about my piano smelling like spoiled milk afterward! Lemon juice might be better for that reason alone. I’d probably hire a pro if ours needed cleaning. (We inherited a 1930s Steinway grand that my grandmother bought herself as a single woman for $1200–a LOT of money back then! She must have been very serious about playing.)
Ivory doesn’t always yellow much naturally, there are 2000 yo Roman & Chinese ivory artifacts that look pretty good and a surprising number of mammoth tusks out there. But the color change patina that does occur can’t be reversed.
Piano keys in particular can get dirty & worn from fingers and paws but the signs would be far more apparent toward the front. Milk DOES readily yellow and stink and, other than being wet, I can’t think of any reason to use it for cleaning anything.