I was searching for some information on 18thC stone cutting methods in reference to diamonds and came across this intriguing story. As an aside, I did a course on jewellery through the ages yonks ago and remembered something about the fact (if I recall correctly) that stone faceting was either a new or relatively new technique around those times. Even so, diamonds were not faceted in the same way as they are today so would have had a much duller look yet would have still sparkled under candlelight. Dining was conducted by the light of candles (and lamps I'm guessing) in those times and the flash of diamonds worn in great numbers by the women (and men) present must have been a sight to see. Diamonds were very popular with those who had the money to spend on them in the 18thC.

It's thought by many that the first event to both rock the foundation of monarchy and also display open defiance of royal authority was the "Diamond Necklace Affair" or the"Affair of the Queen's Necklace".

The Affair of the Diamond Necklace was a sensational, elaborate confidence game involving the Comtesse de la Motte, her husband, Cardinal Rohan, the Parisian jewelry firm of Böhmer and Bassenge, possibly Marie Antoinette, and a diamond necklace valued at 1,600,000 livres. The conspirators' scheme to secure the necklace under the guise of Marie Antoinette's acquiring it through intermediaries began in the summer of 1784, and came to fruition in January of the next year; the ever-complicating drama involved a sham queen, a sham cardinal, and sham royal servants—false assumptions, false signatures, false marriages, and false promises of fabulous wealth—everything was bogus but the diamonds. Arrests were made and an absolutely electrifying trial held in which the cardinal was acquitted, the countess was "condemned to be whipped, branded and shut up in the Salpetrière," and her husband, who had fled to England with the necklace, "was condemned . . . to the galleys for life"
Encyclopædia Britannica

The Affair of the Diamond Necklace and Marie Antoinette's involvement.