New York’s Tiffany & Co. was founded in 1837. The company began modestly as a stationary store. Then, in 1848, a trip to Paris by one of the firm’s founders netted a huge cache of diamonds, which were being unloaded at fire-sale prices by nobles fleeing France’s second revolution. From then on, diamonds remained a key jewel in the Tiffany crown. Tiffany did not cater just to high rollers. In 1858, the company produced and sold pendants...