The one-cent Z-Grill stamp is part of a private collection that will be auctioned on June 14, 2024 (Credit: Robert A. Siegel Auction /CC-BY-SA-2.0)

Acquiring an old postage stamp for millions of dollars might seem extravagant. But the 1868 Benjamin Franklin Z Grill is no ordinary stamp. It is one of only two of its kind known to exist. One is part of the collection at the New York Public Library. The second Z Grill, held by private collector Bill Gross, will be auctioned on June 14, 2024.

Experts at the Robert A. Siegel Auction Galleries in New York estimate the Z Grill to fetch between four and five million dollars. If the stamp sells within that range, it will smash the current US record held by "Inverted Jenny," which sold for $2 million in November 2023. The worldwide record belongs to the British Guiana one-cent Magenta, which went for $8.3 million in 2021.

The one-cent Z Grill is expected to sell for as much as $5 million (Credit: Siegel Auction /CC-BY-SA-2.0)

The stamp's rarity is credited to its "Z Grill," a waffle-like pattern pressed into the paper. This unique feature has an interesting history. In 1868, following the American Civil War, the US Post Office became concerned about people cleaning and reusing canceled stamps.

To prevent revenue loss, officials devised a technique called "grilling." Used until 1870, it created a pattern of small indentations on postage stamps. These "grills" allowed the canceling ink to penetrate the paper, making it difficult to wipe off the ink and reuse the stamp. The Z Grill depicting Benjamin Franklin was one of numerous designs. However, it was only used for a few weeks and rarely on one-cent stamps.

"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," explains Siegel Auctions president Scott Trepel.

The "Inverted Jenny" stamp currently holds the record for the most expensive US stamp (Credit: Credit: Siegel Auction /CC-BY-SA-2.0)

The Z Grill is one of many rare stamps Gross plans to sell at the June 14 auction. His collection, comprising over 100 stamps, is expected to fetch between $15 million and $20 million.

"There’s multiple stamps that’ll bring $500,000 or $750,000, but the (one-cent) Z Grill is the star of the show,” said Siegel Auctions director Charles Shreve. “I just know some people who are lusting for it, and we want to try to get as many people interested in it as possible."