Later this month, the U.S. Mint will release a coin unlike any it's ever made. Instead of being flat, it is shaped something like a bowl, with a convex surface that calls to mind a ball.

A baseball, to be precise.

The design, commemorating the 75th anniversary of the National Baseball Hall of Fame, bears the image of a baseball on one side. The obverse side, as it's officially known, shows a baseball glove, gently curving inward. It's a clever marriage of form and content, with the convex and concave sides lending the ball and the mitt a measure of three-dimensional realism. It's also about as radical as coinage gets, and required an unprecedented effort by our nation's money makers.

"This was like a moonshot for us," says Stephen C. Antonucci, manager of digital development for the U.S. Mint in Philadelphia. "It stretched the bounds of everything we knew about coin development."

One-Upping the French ———————

The curved coin is not, however, the first of its kind anywhere. The bill that birthed the coin–The National Baseball Hall of Fame Commemorative Coin Act, signed into law by the 112th Congress on August 3, 2012–specifically references a curved coin issued by the French Mint, the Monnaie de Paris, to celebrate the International Year of Astronomy in 2009. When Antonucci's team stepped up to the plate, the first thing he did was get his hands on one of those French coins.

A laser scan created a 3-D model of the French original, giving the U.S. team a jumping off point for the general shape of the baseball coin. Despite its dome-like form, Antonucci says, the French coin is fairly two-dimensional in terms of how much its details pop off the surface. He decided that his creation would feature more pronounced relief, adding to the technical difficulty of the undertaking. "My nature's very competitive in these types of things," he says.

>Could a domed die handle the rigors? There was no way to tell until they tried.

Typically, once a design is locked in, the mint sends off for master dies that are used to strike the coin in large quantities. It's a tried-and-true system, but in this case, Antonucci couldn't take anything for granted. Although master dies have stamped millions of coins over the years, every one of those coins was flat. Could a domed die handle the rigors of pressing and tooling? Could flat blanks be wrapped around a domed die in the first place, or would the ball and glove imagery need to be stamped onto pre-curved blanks? There was no way to tell until they tried.

Eric Custer, a product design specialist with the U.S. Mint, at work on the domed coin. Image: U.S. Mint

There was another problem. Antonucci didn't know what was going to appear on the obverse side of the coin.

In addition to specifying a domed shape, the legislation authorizing the coin called for an obverse design selected by a public competition that was still months away. (The winning design, selected in September from a field of 170 entries, was created by Cassie McFarland, a San Francisco Giants fan and designer who lives in San Luis Obispo, California.) Antonucci and his team pondered a suitable design they could use as they experimented with production techniques. The eureka moment came when one team member joked that they were behind the eight ball. Antonucci tasked one of his designers with mocking up a detailed test coin–with a billiard ball on one side and a pool table on the other.

To the Workshop —————

With their billiards-inspired design complete, they took the unprecedented step of CNC milling test dies themselves. "We'd never done that before," Antonucci says. Whereas it usually takes months to get first dies for standard commemorative coins, here the team had prototypes just weeks into the project.

The test runs went surprisingly well. Initially, the plan was to make only the gold and silver coins domed. But at some point, an order came down to make the clad, half-dollar coins (those that, like nickels, dimes, and quarters, have a copper core plated with nickel alloy) were to be curved as well. This was another challenge–Antonucci called the clad coin his "nemesis"–as introducing additional metals increased the risk of warping and die defects. But his team eventually got the kinks ironed out, tweaking the shape of the dome and the severity of the relief to make it all work. This coin is the first clad domed coin produced anywhere in the world.

Dan Perez, a press operator in the Numismatic Division, inspecting a coin. Image: US Mint

The Congressional bill gave the mint permission to issue up to 50,000 $5 gold coins, 400,000 $1 silver coins, and 750,000 half-dollar clad coins. Prices will include an additional charge of $35 for each gold coin, $10 for each silver coin, and $5 for each half-dollar, with proceeds going to the National Baseball Hall of Fame. The coin will be released March 27.

The unique design will likely make the coin a hit with collectors. But for Antonucci, in a world defined by exacting specifications, where every detail is legislated, the dome was a rare chance to push his craft into new territory. The resulting tender, he says, is unlike anything you've held before. "This is gonna change things when you say, 'let's flip a coin.'"