Ivory will take on a character of its own over time.
Cleaning with mild soap (Ivory brand bar soap) and water is fine.
Use a soft cloth, and dry well.
Do not use Polident or any Denture cleaner, it will remove ALL stains and character, and until it starts taking on a patina of its own again, it will look plastic and fake.
Avoid toothpaste, as toothpaste is abrasive and will scratch Ivory, Pearls, Opals and other "soft" stones.
I forget if Hints from Héloise, or Ann Landers some decades ago suggested toothpaste and lots of folks scratched ivory, the metals they were in/on and other nice pcs including pearls and opal rings.
Soft toothbrush, and I mean "soft" , so will Kerlix ( gauze bandage) with the Ivory bar soap assists in getting dirt, and grime out of natural ivory crevices.
It depends on how fine the Ivory is finished out (polished) as to how much dirt and debris will embed in ivory.
Piano Keys are often finished out or polished very fine. [Lapidary]
Ivory is also left in various degrees of "rough" or "not finished out".
My Ivory Stocks, and Knife handles, I preferred a bit of rough texture, as it felt better in my hands and the natural attributes of ivory taking on character is what I liked.
I had yellows and reds and browns and all sorts of character which really looked good, to me.
I received lots of compliments on these as well.
HTH
, but I have multiple sets of ivory 1911 grips, and I clean them with M Pro-7.
