How do I know if pearls are original?

Nacre quality is very important. The nacre is the layers of protective coating — a pearly substance — that grows around a pearl nucleus. The nacre can flake or peel off.

There are myths that determine how to test to a pearl's originality by scraping off the outer layers of a pearl using a the blade of a knife - if no beads are exposed therefore the pearl is original. However, the nacre shall be scraped off - leaving it dull and exposed, and losing it's original luminosity.

Reference: http://www.colored-stone.com/