How does a jewel thief know whether a string of pearls is real and worth stealing?

There may be more than one way to tell if a string of pearls is real, but the great Arthur Barry, a big time thief in the twenties who averaged half a million dollars in thefts per year, had a unique and quick technique.

In the Plaza Hotel robbery of 1925, Barry made off with $750,000 in jewels belonging to Mrs. James P. Donahue, daughter of F. W. Woolworth.

Not only was the theft executed in broad daylight, but Barry stealthily removed the jewels from a dressing table while Mrs. Donahue sat in the bathtub a few feet away.

Among the objects stolen was a rope of pearls valued at $450,000. But the drawer containing the pearls had not one rope but five, four were imitations that the police captain later called “good enough to fool an oyster.” Was Barry’s choice pure luck? Not at all, he rubbed the pearls gently across his teeth.

Fakes are smooth and slippery, he later said, but real pearls give a slightly rough, grating sensation.