An extremely rare U.S. postage stamp from 1868 is up for auction — and it could be sold for up to $5 million.

The New York auction house Robert A. Siegel Auction Galleries, Inc., dubs the 1-cent stamp of Benjamin Franklin as one of, if not ”the most valuable U.S. stamp” in history.

Smithsonian clarified that the stamp is only one of two kinds known to exist. It’s the first time one will be up for sale in 26 years.

Why is the 1-cent stamp so sought after?

Z-grill stamps are the rarest types of stamps for philatelists — or those who study and collect stamps.

According to Smithsonian, grills, or marks, were placed on stamps around this time to prevent them from being reused, and zig-zag patterned grills were the rarest version. The U.S. Post Office stopped issuing the marked stamps in the early 1870s, but some alternate, also rare versions still remain — all of which are claimed to be used and display cancellation marks.

“Most of (the Z-grill stamps) were 2-cent and 12-cent stamps. Some were 3-cent stamps. And very, very few were 1-cent, 10-cent and 15-cent stamps,” Scott Trepel, the president of the auction house, told Smithsonian.

Who currently owns the two stamps?

Fox Business reported that the listed Benjamin Franklin stamp is owned by American investor William H. Gross, who acquired it back in 2005. He is reportedly selling his entire stamp collection to the auction house, which, according to The New York Times, Gross spent over $100 million on.

Auction house director Charles Shreve calls Gross’ collection undoubtedly “the most significant and most valuable collection” of U.S. stamps curated in the past 50 years, per Fox Business.

The other Benjamin Franklin stamp is at the New York Public Library, which was donated the stamp in 1925, reports Smithsonian.

Why is Gross selling his stamp collection?

The investor has been selling off his collection for over 15 years, starting with international stamps in 2007 and U.S. stamps in 2018. He claims to give the proceeds to charity.

A spokesperson for Gross told The New York Times that obtaining rare stamps “took patience, but the chase was the fun part.”

Smithsonian claims that Gross’ complete collection is expected to accumulate up to $20 million.

The stamp can attain a U.S. record

Currently, the Z-grill stamp is estimated to sell between $4 to $5 million. The auction is on June 14 and will end the next day.

If the estimates are correct, it will be the most expensive postage stamp in the U.S., beating out an Inverted Jenny stamp selling for $2 million last fall.

However, a 1-cent magenta stamp from British Guiana — known to be the only one of its kind — sold for over $8 million in 2021, so the Benjamin Franklin stamp may not achieve the world record, per Smithsonian.

Still, the auction house is happy to be a part of the historical event.

“For collectors who have patiently waited for this to happen, it is an opportunity to buy what they have wanted for a very long time,” Trepel said to Fox Business. “And for others who just want one stamp — the rarest of the rare, the best of the best — it could well be an opportunity to capture a trophy.”

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