The jacket in question. William Mebane

To read an interesting piece on not being able to claim a Honus Wagner card fortune, please go here.

Fifteen years ago, David Hunt auctioned off a jersey worn by Lou Gehrig that brought the handsome sum of $85,000. It was a big sale for his memorabilia auction house. But soon after, he received a phone call that hinted at an even bigger score.

"A man said he had a Gehrig jacket and asked if we'd like to take a look," Hunt says. Although he knew that 80% of calls like this amount to nothing, Hunt was intrigued by the tale. The caller's relatives had once lived next door to Lou and Eleanor Gehrig in Riverdale, N.Y., and the jacket was a gift from Eleanor for helping her clean out the house after Lou's death. As it happened, the caller, Dave Ennis, ran a gas station not far from the offices of Hunt Auctions in Exton, Pa., so Hunt paid him a visit. "And out of the closet, he pulls this jacket…"

The blue-black garment was made of heavy wool, its collar and cuffs a faded gray turned slightly green with age, a white felt "N" and "Y" entwined on the front left panel. It looked like a piece lifted straight out of American folklore—as if Mighty Casey were flesh and blood and here was his bat. It hardly seemed real.

And that was the problem: How do you prove that a jacket was once worn by Lou Gehrig and isn't just a musty family fairy tale? It's no idle question. The answer is the difference between a trip to the Salvation Army and a shot at hundreds of thousands of dollars. Anyone who has ever bought an autographed photo of David Ortiz or Albert Pujols on eBay for $50 knows there is a lot of money to be made and spent on baseball memorabilia. A Babe Ruth home run ball can set you back $150,000.

And a Gehrig jacket? That's much more Babe than Big Papi. If it's legit.

The business of memorabilia authentication is dominated by a few firms, notably PSA/DNA Authentication Services of Newport Beach, Calif., and James Spence Authentication of Parsippany, N.J. Between them, these outfits are asked to validate about 400,000 items each year, and they charge between $20 and $500 per exam, depending on an item's rarity. Authenticators compare a signature with an athlete's handwriting samples. They match clothing styles to old newspaper photos and analyze fabrics to pinpoint when they were produced. They study the wear and tear of baseballs to determine their age, and they put them under UV light to see if other autographs have been erased (a ball signed by Ruth alone is worth a small fortune; one he signed alongside other teammates, far less).

Occasionally, of course, greed trumps honor. In 1997, the FBI launched Operation Bullpen to take down a nationwide forgery ring that employed a slew of authenticators to sign off on faked goods. Much of the contraband was small-scale—autographs of modern players—and not the rare quarry that lures serious collectors. Still, the counterfeiters sold up to $100 million of forged nostalgia before they were stopped.

No one authenticates the authenticators. There is no diploma to be earned, no exam to usher them into professional ranks. In the world of high-priced memories, as in the world the mementos chronicle, track record is everything. Authenticators thrive by limiting mistakes. In an industry in which everyone knows everyone else, recommendations—and damnations—are the only checks and balances.

David Hunt is a jack-of-all-trades: memorabilia detective, historian, businessman. Unlike PSA and Spence, which authenticate but have no direct involvement in sales, Hunt auctions the items his company validates and makes money only upon their sale. The onus is on him to build an unquestionable case for his wares. And the bigger the potential price tag, the surer a prospective bidder will need to be of an item's authenticity.

Sitting in the gas station that day, Hunt began to realize what a tough task proving the jacket was Gehrig's would be. First, though, he had to convince Ennis to sell it. Dave Ennis had inherited the jacket from his father, who'd received it from his great aunt and uncle, Raymond and Marion Parker. Eleanor Gehrig had given them a lot of her husband's clothing, actually. Most had been lost over the years, but the jacket became part of the family's identity. Dave called Hunt to slake his curiosity about the piece's worth, but, he wasn't really ready to give it up. Hunt left that first meeting empty-handed, but he started calling Ennis once a year to check in. He'd describe the state of the market and lay out options should the station owner decide to put the garment on the block. And Hunt estimated its value for Ennis: probably more than $100,000, maybe several times that if conditions were right. But Ennis never budged. Then, in late 2007, after more than a decade of dancing, Hunt once again phoned with his annual update. This time, though, he had a wrinkle: A Hunt auction at 2008's MLB FanFest, scheduled for before the last-ever All-Star Game played at Yankee Stadium, would be the ideal setting for this quintessential piece of Bombers history. It would be poised to fetch a maximum price, maybe as much as $400,000. Maybe more. Ennis wavered. To him, the jacket was priceless. But he was 62 and grappling with the financial realities of retirement. Turns out he had a price after all. He signed over the jacket to Hunt for authentication and subsequent sale at the FanFest auction. And his prize possession took up temporary residence in the authenticator's office.

Hunt went to work. These days, some authenticators use DNA tags, viewable with special lasers, to invisibly mark pieces as genuine. Others attach radio frequency identification (RFID) tags to items as soon as a game ends so that forever after they can be linked to that moment in time. But proving this jacket belonged to Gehrig meant dating it to the 1930s, well before the advent of high-tech ID systems. This would require some old-fashioned sleuthing. "It's a filtration process," Huntexplained last spring. "You work backward." He pointed to the inside of the jacket lapel. On the bottom corner of the right flap were two tags. One was a puckered black Spalding label with gold trim. The other bore Gehrig's name in tight red stitching.

"The red is pretty vibrant, and that can be a bad thing," Hunt said. "You start to think, That's pretty red for something 70 years old. But it's on the interior, so there's been no sunlight exposure." Hunt described a Gehrig jersey his company had sold, with a name tag that was much more faded. That tag had been inside the collar, against the back of the neck, so the fading made sense, "because of perspiration," he went on. "If this color is on the outside of a jersey, it's a big red flag that something's up. On the inside, you're okay." Focusing on the Spalding label, Hunt continued with his primer. "Now, if this tag doesn't have puckering, that's another red flag. You want the puckering. It comes from wash wear, from sweat."

Hunt also used photo matching. Consulting old news clippings and team photos, he saw Gehrig had worn a jacket of this style in these colors. But as Hunt pressed on, he began to suspect something more historic: The jacket might be the one Gehrig wore in Detroit's Briggs Stadium on May 2, 1939, the day he took himself out of the lineup to end his consecutive-games streak. If his hunch was right, the jacket was more valuable than he'd imagined. But Hunt needed incontrovertible proof, and he wasn't sure where he'd get it. Then, on a research trip to the Hall of Fame in Cooperstown, he found what he was looking for.

Hunt uncovered an AP photo dated May 2, 1939. The photographer probably took it only because he'd noticed something strange: Gehrig, not manager Joe McCarthy, standing at home plate with the lineup card. And in the photo, Gehrig is wearing a jacket of the same make as the one that was hanging at that moment in Hunt's office.

According to Hunt, most players didn't even have jackets back then. They were expensive, and teams generally didn't spring for them, so only the stars ponied up. And if a guy did have a jacket, it was likely the only one. Then again, what if a chilly Gehrig (average spring temperatures in Detroit in May are in the mid-50s) asked a teammate for a jacket and was tossed an older model from 1937 or '38? Hunt pulled out another photo. McCarthy is in this one, also wearing a jacket. It's the only other shot Hunt found of someone wearing this same style. Brooklyn's player/manager Leo Durocher is in the picture too, and he has a patch on his jersey. A patch known to have been worn for just one season. Guess which one.

"I had a send-off party for the jacket," Ennis says in early July, "for anyone who wanted to see it for the last time." Hunt let him bring the piece home one final time before the July 15 auction. "About 40 people came," Ennis says. "I expected more, but it was summer." His voice trails off. "I'm nervous. I'm hoping it does well, because if it doesn't…I never would have done it."

A few weeks after the party, Ennis and his family are in the Jacob Javits Center in Manhattan. Hunt's space is bounded by glass display cases set up around two dozen rows of chairs. The cases hold sets of early-20th-century cards, Thurman Munson's MVP award, assorted Gold Gloves, ancient pennants, dozens of signed balls and enough jerseys to fill a walk-in closet. In the rear, set slightly apart, is the Gehrig jacket.

The bidding on Lot 860 takes place toward the end of the two-day event. Already, several pieces have exceeded $100,000; a Ruth hat brings $327,750. Hunt offers a few words of gratitude to all involved, then an employee walks the jacket across the stage. The bidding begins at $200,000; paddles wave. Figures are announced and quickly trumped by new bids. More paddle-waving precedes higher figures. In less than two minutes, the bidding hits $325,000.

And there it stalls. Hunt pauses, waits a moment longer…then brings the hammer down. With the 15% buyer's premium—a standard auction commission levied on the floor price—the final number for the garment Lou Gehrig once wore is $373,750, a record for baseball warmup jackets.

Bonnie Ennis rubs her husband's arm as he leans on the back of a chair, looking dazed. "I never should have done this," he says. "I thought it'd go for a lot more. That's what everyone said." Hunt demurs, saying that the winning bid exceeded the minimum reserve price, okayed by Ennis, for which the jacket could be sold. Ennis, now cash-rich but lore-poor, is still upset. "It's gone now," he says with a sigh.

The winning bidder is Gary Cypres, a Los Angeles finance pro and collector who plans to open a museum this fall to house his memorabilia collection, arguably the biggest private sports cache in the world. Cypres, who was born in the Bronx, has a cornerstone from Yankee Stadium, a T206 Honus Wagner card (see page 84) and the ball that, had it not been caught, would have kept Joe DiMaggio's streak alive at 57 games. Gehrig's jacket will reside alongside these storied items. Says Cypres: "I couldn't be more convinced that this jacket is from that day if Gehrig himself came up and said so."