Real pearl necklaces feel warm against the skin, whereas the fakes are cold.mochyn has already mentioned the grittyness of the real thing - a bit difficult if the necklace is around the neck, but if you put a pearl through the teeth it will feel slightly rough - the imposter will be smooth.

For the record, cultured pearls ARE real pearls. They are created through a natural process, just like other pearls. It is just that the irritant is planted rather than a natural occurance.

And also for the record, cultured and freshwater are not two separate types of pearls. Freshwater pearls are often cultured and salt water pearls are often not. And, freshwater pearls are every bit as real as oyster pearls, and have, during certain periods, been more sought after than salt-water pearls.

The tooth test is the very best way to tell real from fake in most cases. Natural nacre is slightly rough. Fake pearls are almost always either glass or plastic, usually with a painted or coated surface. Both of these will be smooth. However, if the pearls are on a woman's neck, you might want to ask her before applying this test.

If you aren't given permission, you might instead ask if you can feel the pearls' weight. Of course, this one, without having had real pearls to hold to test against, won't do you much good. But, plastic is too light to be a pearl and glass is too heavy.

As to the temperature thing, that depends entirely on what the fakes are made of. If you pick up glass pearls, they WILL feel cold. Real pearls don't conduct heat the same way glass does. However, neither does plastic, so they may or may not have that cold-to-the-touch aspect to them. Depends on the plastic and on the coating.

See the good method here http://www.pearl-necklaces-jewelry.com/faq.html