.Tom, I Googled this..
http://www.associatedcontent.com/art...ry.html?cat=24
Use equal amounts of water to lemon juice for the best results. Then wipe with a damp cloth and buff it gently. Be sure to avoid getting any lemon juice on any metal parts of your knives or jewelry. If your ivory is really stained or darkened, you should have a professional whiten it. A jeweler can scrape and polish your ivory without damaging it.
If your ivory needs to be dusted, use a clean, soft cloth, and remove any dust by wiping it gently. To wash dirtier pieces, use a mild soap and warm water. Don't soak knives or jewelry as the glue holding the ivory on can be softened. Use a wool cloth to buff the cleaned piece after it has been rinsed and dried.
If you need to clean ivory piano keys, the process is a little different. Using a dampened cloth dipped in a small amount of baking soda, carefully rub one key at a time. The keys then can be wiped with a clean damp cloth and buffed dry.
Ivory should be kept in a place with moderate temperature and humidity. Frequent changes in temperature, or being too cold or hot, can cause warping and other damage to the ivory. Too much moisture can cause the ivory to mold, as it is an organic material. Your hands should be clean before handling ivory, because the oils from your skin can darken it. For dried out ivory, mineral oil can be used, by wrapping the piece in a cloth soaked in oil, and left to sit for a day or two. Gently wipe the oil off after that.