COOPERSTOWN, N.Y. -- Some of the greatest gems in the baseball world will never see the light of day. The hardest part of the job for the curators at the National Baseball Hall of Fame and Museum is deciding which priceless artifacts belong in display cases and which stay in the archive.

The Hall of Fame has been lovingly sorting through the game's history for 75 years, and only 15 percent of the treasury can be on display at any given time. That means that if there's a few Ty Cobb jerseys out on display, you can be sure there's a few more preserved in a climate-controlled vault.

Erik M. Strohl, the Hall of Fame's vice president of exhibitions and collections, knows the inventory at 25 Main Street better than anyone, and he has a story for virtually every item on the premises. But there's 40,000 artifacts at the Hall of Fame, and it's impossible to let the public see all of them.

"It's part of our mission not just to preserve and save these things, but to share them," said Strohl on Friday during a behind-the-scenes tour of the Hall of Fame's storehouse and archives.

"What good is it if you put it in a room and nobody sees it? Why are you even saving it? That's something all museums and cultural institutions have to struggle with, because preserving things and sharing them are at opposite ends. How do you share them and yet also keep them safe?"

It's a delicate balance, indeed, but one the Hall of Fame has mastered over time. And while the winding scope of the game's history is evident from the many display cases thoughtfully arranged throughout the museum, it's even more obvious when you see the things the Hall has squirrelled away.

The Giamatti Research Center -- named for A. Bartlett Giamatti, the former president of Yale University and Commissioner of Major League Baseball -- is the largest storehouse of baseball information on the planet, and it regularly fields requests for research assistance from students and potential authors.

The library houses a file for every one of the 18,000 players who have made the Major Leagues, and it contains clippings and pertinent tidbits related to their career. This means that if you're Hank Aaron, your file is actually four huge manila folders, and if you had a brief debut, a slim file will suffice.

Another treasure, the old log-books of ancient league statistics, are also on hand at the Hall of Fame. Statistics used to be kept by hand and in ledgers, a laborious process that sometimes allowed human error to creep into the record books. Now, in a computer age, the ledgers are literally history.

Strohl, deep in his element, shows off a couple of the game's most arcane treasures. Here, in a file far from the gaze of the Hall's public, lies the promissory note attached to the sale of Babe Ruth from the Red Sox to the Yankees. It isn't a replica or a reproduction; it's a one-of-a-kind relic of the most fateful transaction in league history.

Strohl, from another file, pulls a baseball rulebook dating all the way back to 1859. Back then, he said, you paid to play baseball instead of it being the other way around. Belonging to a baseball club was like being part of a country club, and that's why baseball locker rooms are called clubhouses to this day.

So where do all these items come from? Fittingly, they come from all over. Strohl said that players are contacted in advance of certain milestones to see if they'd be willing to donate some equipment to the Hall of Fame, and he said that teams and fans alike are active custodians of the game's history.

"We get artifacts from teams, from players and from fans," he said. "I tell people all the time, even kids when they're on the tour, 'Once we accept something, we accession it. You formally donate it. You surrender ownership. You give it to us ... and we promise to take care of that thing forever."

And when he says forever, he means it. The Hall of Fame has four climate-controlled archives, each one set to a different climate to best preserve the artifacts. One of the vaults is devoted to paper and another to photographs, and a third one houses a multimedia library of film, video and recorded sound.

The fourth archive, museum collection storage, is Baseball Heaven. Row after row of meticulously kept closets hold jerseys, bats and gloves of the greatest and most notable players to ever play the game. Cobb, who set nearly 100 records during his career, has eight game-worn jerseys at the Hall.

Those artifacts -- some more than 100 years old in Cobb's case -- are kept folded in boxes, preserved for a future day to be pulled out and shown to the public. It's a warehouse of priceless baseball memorabilia that will never be auctioned and never be sold as long as the Hall of Fame exists.

And if the jerseys strike your fancy, there's something even closer to the heart of the game right around the corner. The storage room houses four giant lockers full of bats from all of the game's iconic sluggers, starting before Ruth and winding all the way to present-day stars like Ichiro Suzuki.

These items, hidden but not forgotten, are the heart of the Hall of Fame's collection. And sometimes they're roused from their slumber to be shown to the public. The Hall runs a program called the VIP Experience that allows fans to get a backstage tour of the library archive and a view of old artifacts.

The VIP Experience will be held six times between February and May of next season, and interested fans can find information at baseballhall.org. And if a tour's not enough, fans can even spend an evening at the Hall of Fame as part of the museum's Extra Innings Overnight experience.

The Hall of Fame's next class of immortals will be announced over the course of the next month, and thousands of fans will make a trip to the July 27 induction ceremony. Group by group, they'll file through the plaque gallery and linger near their favorite legends, and the Hall will make sure that tradition keeps getting richer.