Sunday, November 14

Following in Cleopatra's footsteps

You probably already heard of the story of Cleopatra VII (69 B.C. - 30 B.C.) and her most extravagant feast. To show off her wealth and power, she challenged Marc Antony, the Roman leader, that she could host the most expensive meal in history. The feast she had arranged was extraordinary in its finale. Cleopatra removed one of her pearl earrings and tossed it in a goblet of wine vinegar.

© British Museum, William Kent,
Cleopatra dropping the pearl into the wine

The pearl was extremely rare. Not only it was natural, but also very large, which made it of an extraordinary value. Roman naturalist and philosopher Pliny the Elder (23 - 79 A.D.) in his Natural History describes it as "the largest in the whole of history". Some say that at that time it was worth “the value of 15 countries”. The pearl dissolved in the vinegar, which Cleopatra then drank. Needless to say, Marc Antony had to admit his defeat in their bet. According to the legend, the other pearl from Cleopatra’s earrings was later cut in two, with each half placed in the ears of the statue of Venus in Rome.

Could Cleopatra really dissolve a pearl? We decided to verify how pearls respond to vinegar, or any other acidic solution for that matter. Pearls are mostly calcium carbonate, which is susceptible to even a weak acid, such as the one found in dressings or fruits. To test this, we decided to sacrifice one of white round stud earrings.

In our experiment, we used regular white vinegar, just like the one you can find in supermarkets all over the World. It is similar to the one used in the ancient Greco-Roman world, therefore our test closely follows the ploy that Cleopatra used to impress Antony. Then, we took photos of the pearl to see the rate of deterioration of the pearl surface. Here are the results of our tests:

Pearl and vinegar test (click to enlarge)

As you can see, in the first photo the pearl is round, lustrous, and flawless (we drilled the indent to get more insight into how fast the pearl would shrink). After one hour only, the pearl exposed to the acidic solution loses some of its luster and becomes smaller. This is because the crystals of calcium carbonate, from which pearls are made, are being decomposed by acid into calcium acetate, water and carbon dioxide. This process leaves small specks of translucent, gelatinous material on the surface, just like the one pictured below:

Formation of calcium acetate

There is a name for the residue obtained from the precipitate of an acid solution - a magistery. The magistery of pearl, drunk by Cleopatra in toast to Antony, was thought at that time to be a potent aphrodisiac, probably because pearls were associated with Venus, the Roman goddess of love and beauty, also born of the ocean.
We managed to obtain a small portion of the magistery of pearl:

Magistery of pearl

What are the lessons learned? Always wipe your pearls after them come in contact with acidic solutions, such as acidulous foods, fruit juices, or salad dressings. If possible, remove your pearl jewelry before you prepare any food. The smallest splash of you favorite tomato sauce and you may involuntarily end up with a helping of an ancient love potion...

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