I once had to clean an old collection of over 700 ivory pieces,
mostly elephant, some narwhal, some bone. Be VERY careful when
attempting to clean ivory. First, make sure it IS ivory and not bone
or an imitation.
Black spots on ivory are usually caused by mold, in turn caused by
keeping the ivory piece in a damp atmosphere. Ivory is quite porous
and will rapidly absorb anything placed on its surface. Here's the
guidelines I've always followed, with attribution.
Never attempt to remove the surface coat pigment or patina, as it
affords protection for the piece, and is an indication of age. Many
liquids, including water and cleaning solutions, are destructive to
ivory, and should be avoided. Applying water may cause swelling and
cracking. Extremely dirty pieces should be referred to a
professional conservator, as well as pieces that are dyed, pigmented
or inlayed. When in doubt, consult with an expert.
Dry cleaning methods may be attempted: Using a clean, soft paintbrush
or toothbrush, carefully brush dirt off the object.
Ivory that is in good condition should be cleaned and wiped gently
with a soft, clean cloth. If dirt remains, but no cracks, using a
solution of 50% ethyl alcohol and 50% distilled water, dip a Q-tip
into the solution and blot on a piece of paper towel. Use this to
clean a small, inconspicuous area, and dry immediately. If this goes
well, clean the entire piece in this manner, working on one small
piece at a time, and drying immediately.1
Remember: When in doubt, consult with a professional.
1 The Cane Collector's Chronicle, Volume 4, Number 1, January,