(NEXSTAR) – A mint condition Mickey Mantle baseball card recently sold for $12.6 million, becoming the most expensive piece of sports memorabilia on record. It broke the previous record set in early August during a private sale when a Honus Wagner card went for $7.25 million. A Wagner card set the record before that in August 2021, selling for $6.6 million.

It’s no secret that baseball cards – and sports memorabilia – have become a booming business over the last few years. In some cases, the trading card market has become so hot and the desire so great that retailers like Target had to restrict access to their trading card department. 

During the first half of 2021 alone, eBay reported $2 billion in trading card transactions occurred on its site, with an average of one sports trading card being purchased every second.

But what is it that has caused the aforementioned Mantle and Wagner cards to sell for a cumulative $26.45 million?

Well, it’s all in the cards.

Wagner and Mantle are part of a trio of card sets considered the most desirable in sports collecting, Mike Provenzale, a production manager with Heritage Auctions told Nexstar. Those sets are the 1909 T206, the 1933 Goudey set, and the 1952 Topps set.

The 1909 T206

The first, the 1909 T206 set, was found in cigarette and tobacco packs from the American Tobacco Company. Notably small compared to modern cards, Provenzale referred to the run of cards as the “first landmark set.”

“That one is all about rarity,” he said, referring specifically to the Wagner card from that set. Only about 60 cards are known to exist, and “most of them are in horrible condition.”

Wagner is widely revered as one of the greatest players of all time. He was a shortstop who played primarily with the Pittsburgh Pirates during his 21 seasons and was among the first five players inducted into the Baseball Hall of Fame in 1936.

Now, 105 years since Wagner took the field, his T206 cards are bringing in millions of dollars at auctions. Due to their rarity, cards graded authentic – meaning they’re in worse condition than what is covered on the traditional one-to-10 scale – still have the potential to sell for millions of dollars.

The rarity surrounding Wagner’s card is often attributed to two stories, according to Provenzale. One is that Wagner, though a heavy tobacco user himself, didn’t want his card to be used to promote tobacco use among children. The other is that he wanted to be compensated for the company’s use of his image, an unusual request in the early 1900s. It’s still unclear why exactly Wagner cards are so hard to find.

The 1933 Goudey Gum set

While Wagner’s era of baseball cards were used to promote tobacco products, the 1933 Goudey set relied on a different product – gum. The Goudey Gum Company set out to create “a really incredible line” of cards to advertise their product, Provenzale explained. And while they accomplished their goal, making “one of the most aesthetically pleasing sets,” poor timing nearly hampered their success.

The set was released amid the Great Depression. But for just one cent, they could purchase a piece of Goudey Gum and get with it a baseball card. It worked – between 1932 and 1933, the company’s profits are said to have tripled, Provenzale said.

Some of the most well-known players, specifically Babe Ruth and Lou Gehrig, can be found in the 1933 Goudey set. Another, Hall of Famer Nap Lajoie, was said to be card number 106 in the set. But, in another brilliant marketing ploy by Goudey Gum, you could only get his card if you sent a letter to the company asking for it.

Ruth and Gehrig are valuable, but Lajoie carries a special worth. The majority of his cards carry a paperclip imprint on the top after being attached to the letter, according to Provenzale. A Lajoie card recently sold during a Heritage Auction went for $114,000. In 2019, a worn and tattered Ruth card from this set sold for just over $4,000. While cheaper in comparison to the Wagner and Mantle cards mentioned before, this card was graded as authentic.

The 1952 Topps set

Nearly two decades after Goudey Gum, the 1952 Topps set hit the market. These cards were the first that looked like the cards we’re now familiar with – the size normalized, stats were added to the back, and facsimile signatures were added to the front.

In addition to Mantle, considered the most popular of the 1952 Topps set, other cards include Willie Mays and Jackie Robinson. Mays and Robinson are valuable, Provenzale explained, but Mantle leads the pack.

This is largely due to how cards were released. At the time, cards were released in series. One-fifth of the cards were released before the season, a second round was released at the start, and so on through the season.

Mantle, a New York Yankee and “the face of 50s baseball,” was card number 311, Provenzale said. That put him in the final series but, because of production delays, that series wasn’t released until after the season had ended (and after the Yankees beat the then-Boston Dodgers in the World Series). The final round of cards didn’t sell well and most sat in a warehouse for over a decade.

The remaining cards from the series, including Mantle’s, were then loaded onto a barge and dumped into the Atlantic Ocean, according to Provenzale. Still, more examples of Mantle’s card are known to exist than Wagner’s.

What about error cards?

There is a particular subset of cards that many collectors thought would be incredibly valuable – those with an error.

“But, that isn’t always the case,” Provenzale explained. One of the most well-known error cards is that of Cal Ripken’s brother, Billy Ripken. He was initially photographed holding a bat that had an obscene phrase written on the bottom of the bat that went unnoticed at first. After Topps discovered the error, the original cards were pulled off the market and replaced with an edited version. Cards that aren’t edited can go for a couple hundred dollars, according to Provenzale.

Some error cards are lucky enough to be worth more than three figures. Provenzale noted another from the 1909 T206 set, Sherry Magie. When the cards were printed, they misspelled his name as ‘Maggie.’ Being that the card is unique and from one of the most iconic card sets, Provenzale said it could “do high five figures.”

What’s next?

But what about today’s market? Is there a card today that will be the next Honus Wagner or Mickey Mantle?

It’s possible. Previously, many cards were mass-produced, especially in the 1980s and 1990s, Provenzale explained. Manufacturers have created their own rarity, sometimes making cards known as ‘one to one,’ meaning they’re the only one available.

“Those one-of-one cards do sell for six and seven figures, even though it’s just manufactured rarity,” Provenzale said. Rookie cards can be largely valuable as collectors “love the book ends,” or those from the beginning and end of a player’s career.

If you have any of the previously mentioned cards, or your own set you feel could be of value, it’s important to do your research before rushing to sell. Experts at your local card shop or sports memorabilia store can help appraise your item, as can those with auction houses like Heritage Auctions.

Be wary of where you’re selling, though. Some shops may offer you less than what the card is worth in order to make a profit on it. Other outlets, like auction houses, where the percentage they keep is based on how much your card or item sells for. Online retailers like eBay, which has its own service to prove authenticity, will work in the same fashion.

The Associated Press contributed to this report.