Gary Eldon Lea made the discovery of a lifetime two years ago at an estate sale in Spring Valley, Minn.

It was a 13-by-8-1/2-inch copper plate created in 1775 to print currency for pre-Revolutionary War New Hampshire.

The colonial government hired silversmith John Ward Gilman to design the plate and print the money in denominations of 1, 6, 20 and 40 shillings to help fund the war against the British.

After he learned of its potential value, Lea, 60, arranged with Heritage Auctions Inc. to sell it in Boston in August 2010.

The starting bid: $50,000.

But on the eve of the sale, the state of New Hampshire said: not so fast.

The plate was “a one-of-a-kind colonial antiquity” that belonged to New Hampshire, the state’s attorney general said in a court filing.

“Once it is state property, it’s always state property, unless the state disposes of it properly in some way,” said Peter Roth, assistant attorney general in New Hampshire. “We couldn’t find any record that that had happened.”

New Hampshire asked Lea to take the plate off the auction block. He did.

Two days later, Lea asked the Fillmore County District Court in Minnesota to declare him the exclusive owner. New Hampshire moved to dismiss the action for lack of jurisdiction, “because under applicable law it doesn’t make sense to make a foreign state come in and be under the jurisdiction of another state’s court,” Roth said.

Fillmore County District Judge Robert Benson ruled in Lea’s favor. But Monday, the Minnesota Court of Appeals reversed that decision and sent the case back to the lower court to reconsider the jurisdiction question.

Lea, an amateur coin collector, lives in Peterson in southeastern Minnesota and works for the local school district.

His attorney, Bennett Myers, said many collectors spend hours poking around garage and estate sales. Most find nothing of real value.

“When they hit a home run, is it only then that these other parties step out from the woodwork and claim it was theirs all along and attempt to take it away?” Myers asked.

He said he and Lea are disappointed in the appeals court decision, but he said it “does not close the door on the district court’s jurisdiction to decide the case.

“Instead, it instructs the court to determine several issues which it has not yet had the opportunity to consider,” Myers said.

If the district court decides it does not have jurisdiction, Lea’s case – his attempt to confirm ownership of the copper plate – would be dismissed.

According to the Heritage Auction catalog, the copper plate’s designer came from a distinguished family of silversmiths.

A document unearthed by a New Hampshire state archivist shows the colony paid Gilman 13 pounds to create the plate, prepare the press and print the currency.

His itemization of his tasks included “11 shillings 3 pence for a carriage with driver to transport the press from Newburyport to Exeter.”

Gilman also charged the colony for 24-1/2 days of labor for himself and his brother, Benjamin.

“New Hampshire declared statehood in September 1776,” Lea’s attorney wrote in his brief to the appeals court. “Therefore, it is unknown whether the copper plate was ever the property of the state of New Hampshire.”

It re-emerged in the 1850s as part of the collection of a prominent physician in Baltimore. No one knows what happened to it until it appeared again in October 2009 at the estate sale in Spring Valley.

The copper plate is being held at a secure location in Minnesota, Myers said.

Emily Gurnon can be reached at 651-228-5522.