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FORT LAUDERDALE (CBSMiami) — During World War II, copper became a scarce commodity needed for the war effort.

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It forced the U.S. Mint to experiment with alternative materials, like steel, plastic and rubber, to produce the one-cent coin, more commonly known as the penny. Since 1792, pennies had been made of copper.

However, one such alternative involved an all-glass penny, manufactured in 1942, by the Blue Ridge Glass Company in Tennessee.

It was a short-lived experiment, and a failure, and only two are known to exist today. One of them is broken in half.

The other is expected to sell for $30,000 or more at a public auction in Ft. Lauderdale, hosted by Heritage Auctions, on Thursday, January 5th.

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“The present 1942 glass experimental piece is the only intact example discovered in nearly 75 years since the experiments,” said Mark Borckardt, Senior Numismatist and Cataloger at Heritage Auctions. “Although glass was never used for emergency U.S. coinage, this piece represents a unique artifact of the ingenuity and determination of Mint officials and private industry.”

The rare coin is made of tempered, yellow-amber transparent glass. It was re-discovered in 2016 by Roger W. Burdette, author of the book United States Pattern and Experimental Pieces of World War II, but its history remains a mystery.

“We know that before doing any of the work, Blue Ridge Glass had some of the employees carry some of the blanks in their pockets for a few days as a test, but the blanks chipped and created sharp edges,” Burdette said. “I think it would have been tough for the public to accept them as money.”

By the time the glass coins were ready for distribution in December 1942, it was already too late for the U.S. Mint to consider them as a viable replacement for the penny.

Today, pennies are made of zinc and copper-plated, giving them the familiar look Americans are used to.

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The coin is one of the highlights of a multi-million-dollar public auction of rare coins and paper money in the Heritage auction, coinciding with one of the country’s largest coin collector’s events, the Florida United Numismatists convention.