I have some mammoth ivory rings (on a flute, but I post here because I think more pipes have ivory than flutes) that got a little discolored from the lining of the case. Blue dye, I’m guessing.
Would it be OK to dab bleach on the ring carefully with a Q-tip? Is that crazy?
The part before the section I’ve quoted discusses various kinds of ivory, including mammoth ivory, so I assume that the instructions work for all kinds.
CLEANING IVORY
A representative of The International Ivory Society suggests mild dishwater soap and water. Wash, rinse and dry ~ do not soak. Deep stains, such as paint, ink or oils probably cannot be removed as ivory is porous and absorbs these materials. Some old ivory necklaces and bracelets are seen with a pinkish or reddish tinge which was absorbed from the henna dye used on the skin of the wearer.
Here is a link to a another site, which advocates non-fluid cleaning methods and is well worth reading if you are attempting cleaning:
Ivory was traditionally polished with whiting ( French chalk) and a little oil ( almond ) on a cloth. I have polished ivory with toothpaste successfully too though the minty odour could cause comment!