Think you have an genuine IVORY? Here's some simple tips to help you identify true ivory versus bone and plastic:

• Get or use a jewelers loop (or a good magnifying lens) and study the item carefully. You will be looking for little streaks or pores known as "Haversian System" which, if the signs are all there, indicates that it is bone, not ivory.
• Bone and Ivory weigh more than a synthetic material such as celluloid which is oftentimes confused as ivory. "Knock" on the item and listen carefully... bone and ivory will sound less hollow than plastic or celluloid. Plastic has a different sound when it's tapped versus bone and ivory.
• True ivory will yellow naturally with age. The darker the color, the older the ivory is. However, be careful when looking to buy an item that's been identified as "antique ivory" as there are people out there who will try to take ivory and darken it using tea or other means to make it appear older than what it really is. There is an easy way to tell if it's been artificially aged: Take some saliva on your fingertip and rub the ivory. If color comes off on your finger or the area you cleaned is lighter than the rest of the item then it's been colored to fake it's age. This will only work with saliva.
• Another surefire way to tell between bone and plastic versus ivory is to take a needle and burn it with a lighter until it's red hot. Then take the needle and touch the ivory in a non-conspicuous spot. True ivory cannot be burned but if it's bone or plastic a burn mark will be left. This tip was given from an episode of Flea Market Mania.
• Hold the ivory up under strong lighting and look closely for a "cross hatch" or wavy pattern. If you can see it then turn the angle 90 degrees and check again. If it's true ivory you will be able to see it the first time but not be able to see it once you turn the angle 90 degrees. It will also appear as a pearlescent.

This picture is a true ivory tile....

Now, here is a picture of bone tile (notice the pores and the Haversian System?): 

And here is a picture of a celluloid tile (notice the fine vertical lines that are there to make it look like ivory? The graining pattern is too "regular" to be ivory: