History doesn't tell us Mary of Burgundy's reaction when Maximilian of Austria gave her a diamond engagement ring in 1477.

But if a modern-day Max were to slip a similar ring onto the hand of an '80s Mary, the chill might go all the way to her feet.The stones in the ring presented by Maximilian were somewhat small and dull, by current standards, but that modest ring holds a special place in jewelry history, experts say. It was probably the first diamond engagement ring.

"They don't have that fire to them," says John Loring, design director at Tiffany & Co., whose famed Tiffany setting remains universal nearly 100 years after its development.

A copy of Mary of Burgundy's ring has been on display in a special exhibit, "The Power of Love: Six Centuries of Diamond Betrothal Rings," tracing the history of a girl's best friend.

"This gives you a sense of where it all started," says Benjamin Zucker, gem dealer, author of the book "Gems and Jewels" and primary organizer and supplier of the recent exhibit at Christie's, which continues on a worldwide tour following its close here.

It also shows where it ended up: large, dazzling stones with 58 facets - the "brilliant cut" that most effectively reflects and disperses light.

In between, the development of cutting is seen, from the dull "hogback" cut - actually just a polished-down point of the rough stone - to the rose cuts and square cuts of the 18th century.

Settings vary from simple to elaborate, reflecting increases in jewelers' skills as well as the supply of diamonds.

Among the landmarks of love in the exhibit is the heart-shaped engagement ring given to Elizabeth Barrett by Robert Browning.

Prints of centuries-old paintings show the diamonds of old - appearing basically black.

"If Mary of Burgundy and Maximilian could have walked into any New York City jeweler's, they would have been dazzled indeed," said Zucker.

Dazzled because diamonds of their day could not be cut, and so were left in the natural octahedral form, or worn down with diamond dust into the hogback, or table-top, cut.

But they were rare, coming almost exclusively from India, and treasured for their hardness, Zucker and Loring said.

"Diamonds don't go away," Loring said. "Some of these modern diamonds are hundreds and hundreds of years old - they've been cut and re-cut."

Because of that durability, and "because they're white and pure," Loring said, diamonds are the natural choice as a symbol of betrothal.

By the 18th century, India's supply was running out, but in 1725, it was noticed that miners in Brazil were using diamonds as chips in card games, Loring said. Diamonds suddenly became plentiful and their use in jewelry "more and more lavish."

Discoveries in South Africa in the 1860s, then later in Botswana, Australia and the Soviet Union, have kept the supply steady, he said.

Diamond rings remain as popular as ever, according to Zucker and Loring. The Tiffany setting remains the favorite, its tiny prongs holding the stone aloft for maximum fire and brilliance, Loring said.