Instructions
Examine the size and shape of the item. The average walrus tusk is 14 inches long. A tusk of much greater length would be a prized rarity and should therefore be treated with suspicion, and considered as a possible fake.
Inspect the tusk for any cracks. Real ivory often warps some with age. The presence of cracks is often a sign of authenticity. However, it is not a definitive one, as some fakes have cracks to help create a more authentic appearance.
Look at the color of the piece of ivory. Resin fakes tend to be either extremely pale or to have been stained an even yellow-brown. Fakes ivory often has a consistent patina. Real walrus ivory will have a more complex patina, with the stains tending to follow the path of cracks and/or blemishes. Real ivory is not perfect and contains blemishes, this is another identifying factor.
Turn the tusk in the light. Like wood, real ivory has a delicate grain. This is something that the manufacturers of resin fakes have not managed to reproduce.
Heat up a pin and insert it into the base of the tusk. If there is a puff of smoke and an acrid smell, then you're holding a piece of resin.