A version of this article first appeared in CNBC’s Inside Wealth newsletter with Robert Frank, a weekly guide to the high-net-worth investor and consumer. Sign up to receive future editions, straight to your inbox.

A $484 million art loan secured by billionaire Leon Black and disclosed in the latest Epstein files highlights one of the fastest-growing and most lucrative corners of the art world.

According to a March 2015 document released as part of the Epstein files, Black secured the loan from Bank of America backed by works of art. While not unusual for top private banking clients, the loan made headlines for its size and the exotic collateral, which included blue-chip works by Picasso, Giacometti, Titian, Matisse and others.

Art lending, however, has become an increasingly valuable tool for both wealthy collectors and the wealth management firms vying to manage their fortunes. The global market for art loans is estimated at between $38 billion and $45 billion today, according to a report from Deloitte and ArtTactic. The market is expected to top $50 billion by 2028, growing at about 12% a year.

Adam Chinn, managing partner of International Art Finance and longtime art-finance expert, said art loans are a way for collectors to pull cash from paintings that they can also continue to enjoy on their walls.

“It’s the best of both worlds,” Chinn said. “You can monetize an otherwise non-income producing asset. And it’s still great to look at.”

Far from signaling a lack of funds, art loans are typically used by the wealthy to provide ready cash, leverage financial investments and avoid hefty tax bills. Private banks often grant art loans to top clients at low interest rates, knowing the client has hundreds of millions or even billions in other assets in case the loans default. The interest rate on Black’s loan in 2015 was 1.43%, according to the document.

The bulk of the art lending market is dominated by the auction houses – especially Sotheby’s Financial Services – as well as specialty lenders like International Art Finance.

Scott Milleisen, global head of lending at Sotheby’s Financial Services, said collectors use the proceeds for a wide variety of purposes. The company now lends against classic cars as well as art.

“Many of our clients borrow against their fine art collections to invest in businesses, pursue new art acquisitions, or release cash without selling works they love,” Milleisen said.

Chinn said many of today’s collectors are top leaders in private equity and hedge funds. Since they’re used to using leverage to turbocharge their wealth in their investments and businesses, they view leveraging their art collections as a natural extension. Chinn estimates that the total value of art held in private hands is between $1 trillion and $2 trillion. With art loans representing a tiny fraction of the total — well under $50 billion — he said the industry has plenty of room to grow.

“Art is the most under-leveraged asset on the planet,” he said.

Art loans also generate lucrative tax benefits. Selling a work of art triggers a capital gains rate of 28% — a higher rate for collectibles than other categories — along with the 3.8% net investment income tax, bringing the top rate to 31.8%. Selling in certain states also triggers state taxes.

An art loan even at today’s elevated lending rates, typically around 8% to 9%, is still far more efficient that paying a tax. Plus, borrowers can usually keep the art on their walls.

The art lending business has also benefitted from a 2017 tax change that eliminated the use of so-called 1031 exchanges in the art market. The practice allowed art collectors to avoid capital gains taxes by swapping one work for another. Without the benefit, many collectors have turned to loans to provide liquidity without the tax penalties.

Chinn said that given the art market’s recent rebound, and falling interest rates, art lending is poised to continue its strong growth.

“The art market is a strange market,” he said. “But if you look at every other asset class, eventually it gets fractionalized, securitized and leveraged. It’s just the nature of the universe.”