Back in 2006, as Glenstone, a private art museum in the Maryland suburbs of Washington, was preparing to open its first exhibition hall, curator Emily Wei went to Mitchell Rales, her billionaire boyfriend and the guy footing the bill, with a proposal: She wanted him to actually explain his vision for the museum to the press.

“He’s like, ‘You don’t understand, do you? I haven’t given an interview since 1984. I’m not going to start now,’ ” Emily, now 42, recalls. “So we had this fight because we didn’t know each other that well.”

“It wasn’t really a fight,” says Mitch, now 62.

“It was a disagreement,” says Emily. “He was irritated by my suggestion, so I was like, ‘Okay, fine, I’m glad we had that discussion.’ ”

Twelve years later, as they sit for an interview, Mitch’s reticence remains. But it’s clear that Emily Wei Rales — they were married in 2008 — has, over the years, persuaded him to become more willing to tell his story. In 2012, Mitch broke his self-imposed three­ decade media blackout and talked to The Washington Post. His motivation, he tells me, was simple: to explain to those suspicious of the closed-off collector that Glenstone is in fact meant to be his great gift to the public.

Now, the pair is about to reveal a major reinvention of their Potomac, Md., institution. What was once a single building has been transformed into a sprawling, 230-acre campus of art and nature.

The idea is for Glenstone to no longer be one of the best-kept secrets in the Washington area. It is to show off what many consider the greatest private collection of American and European contemporary art in the country.

The core of the new Glenstone — set to open Oct. 4 — is a building of interconnected pavilions designed by architect Thomas Phifer. This adds 50,000 square feet of galleries to the 9,000 square feet in the original exhibition hall. Glenstone’s landscape has been remade, with more than 8,000 trees planted, a network of paths created and even a stream restored. The collection of art, meanwhile, is up to 1,300 objects.

Mitch — worth about $4 billion, according to Forbes — has resisted revealing the overall cost of the expansion, almost out of habit, though he now concedes that the price tag is around $200 million. And yet money may be the least interesting thing about Glenstone. Lots of rich guys, after all, are into art. And private museums — from the Isabella Stewart Gardner Museum in Boston, to the Barnes Foundation in Philadelphia, to the Frick Collection in New York — are part of an American tradition. Glenstone, however, has always been quirkier than other venues. Inside, you’ll find some predictable big names — Calder, Rothko, Pollock — but also works of artists who are rarely collected by museums in such depth: Michael Heizer, Jason Rhoades, Roni Horn, Charles Ray, Louise Bourgeois, Robert Gober. “These are not trophy artists,” says Iwan Wirth, the Swiss-born president of Hauser & Wirth, one of the most influential galleries in the world. “They’re not collected by groups of collectors. They are highly individual.”

As for the collectors themselves, even though they’re now agreeing to talk, they would prefer not to be the center of the Glenstone story. The personality stuff, the auction house buzz, the money all take away from the bigger idea: At a time when so many museums are looking for ways to be flashier and more “relevant,” Mitch and Emily Rales’s intent is to turn these rolling hills not far from the Potomac River into a shrine and an oasis, a quiet destination where future generations will see the masterpieces of our time long after the Raleses are gone.

“The personal needs to be separated from the institutional,” says Emily, now Glenstone’s director and chief curator. “People are very curious about how the super-rich live. We’re not about to change that, and it’s the life that we have, whether we like it or not. But the truth is, that has nothing to do with Glenstone.”

That's not exactly right, of course. The billions Mitch Rales has earned over the decades have paved the way for Glenstone's existence — and he is eager to spend them. Indeed, when he talks about the funding mechanism for Glenstone, he talks about being in the "capital reallocation business." "What I mean by that is we're not leaving the Earth with any money," he says. "When we go, there's not going to be money bestowed on children and grandchildren in any meaningful way. This is about reallocating the money we had the good fortune of making to other causes."

There is a model for this: his father, Norman Rales. When Norman was 7, his mother died giving birth to one of his siblings. It was 1930, and Norman’s father was overwhelmed. He had the boy and two siblings placed in a Jewish orphanage in New York.

Norman never went to college, but he started what became the Mid South Building Supply Co. in 1965 and moved with his wife, Ruth, and four young sons from Pittsburgh to Washington. Later, as business boomed at Mid South, Norman would reward the company’s biggest clients by chartering a plane to take them on island vacations. He also bought a piece of the Texas Rangers. And in 1986, he started a family foundation that has provided tens of millions to hospitals, school programs for disadvantaged children and cancer research. Josh Rales, the youngest of the four sons, notes that “if you go to the King David cemetery in Northern Virginia and you look at the plaque where my dad is buried, it says that he was a champion for the underdog.”

Norman “did not give us a penny,” says Mitch, though he and his older brother and business partner, Steve, have come to believe that their father did secretly help them get started. In 1981, the brothers needed to borrow $1 million to buy their first business, a vinyl siding company. They were able to secure a bank loan on their signatures alone, leading them eventually to believe that Norman had personally guaranteed the loan. “I don’t know that for a fact, but it’s my theory,” Mitch says. “Because that’s my dad. He would never want anybody to know that he helped us.”

Mitch, who had been a standout athlete at Walt Whitman High School in Montgomery County, Md. — the captain of both the football and baseball teams — partnered with Steve in 1984 to turn a defunct real estate company into the Danaher Corp., naming it after a waterway in Montana where they had enjoyed a particularly good guided fishing expedition. They started small, with a series of leveraged acquisitions, but eventually, with increasing reserves, expanded into a Fortune 100 global science and technology company.

It’s easy to mark the exact date when Mitch Rales, generally outgoing and driven, became Mitch Rales, the reclusive, privacy-obsessed billionaire. On Nov. 18, 1985, Forbes magazine published a 1,182-word article titled “Raiders in short pants.” The story portrayed the brothers as merciless takeover artists and “callow youths” whose main business strategy was to dodge taxes. Forbes compared them to real estate speculators who buy buildings cheap, “kick out the old ladies” and then resell the properties for twice their original value.

Funny thing is, Mitch wasn’t even quoted in the story. Only Steve was. Yet Mitch refuses to forget the article, like a supermodel carting around her gawkiest middle-school photo as if to keep herself in check. He mentions the Forbes story early in a recent interview at Glenstone, quoting the headline. His friends, old and new, have heard about it.

“Mitch told me about the article,” says Sandy Rower, president of the Calder Foundation. “He just felt burned, and they just decided that was it. It certainly didn’t help their business to have their face out in the world. To buy a new tooling company it didn’t matter to be a celebrity.”

Emily’s encouragement wasn’t all that changed his attitude. Ten years ago, the Washington City Paper published “A Very Private Collection,” a story about Glenstone. Rales, as always, declined to speak to the writer, in this case Angela Valdez. She, in turn, viewed every element of Glenstone — the discouragement of press coverage, the fencing that marked the property, even the no-gum-in-the-gallery rule — through the lens of a John le Carré novel. With neither Rales willing to explain the vision, Valdez spent considerable space questioning whether Glenstone was simply a rich guy’s tax shelter.

“To say it was irritating would be an understatement,” says Mitch. “Maybe it’s just another great example of a lesson learned through the process. We all learn from mistakes. I’m not sure we could have turned the City Paper around, but at the end of the day, we at least will be able to show this building to the press, and people will make informed judgments.”

On a midweek summer morning, Emily Rales leads a group of trainees through the museum's Louise Bourgeois exhibition. At most museums, the guides are either older volunteers called docents or part-time guards paid hourly. At Glenstone, the Raleses launched the Emerging Professionals Program. Those selected from a pool of recent college graduates are brought on for two years, with a salary, health insurance and a day off the floor each week for professional development. The idea is to help provide a start for bright, aspiring curators who don't want to face grad school bills.

“Most recent graduates from any art history program will start with an unpaid internship and then pile on unpaid internship over unpaid internship and just keep going until finally a real paying job comes up, but by then they’re saddled with all this student debt,” says Emily. “What ends up happening is that it favors a certain class of person. So how does that look?”

The group following Emily around the gallery looks to be diverse and, indeed, they’re from as far away as the University of Wyoming, as close as Virginia Tech. They are black and white 20-somethings holding pencils as they scribble down notes. They crowd around as Emily points out special details about Bourgeois’ work. They have already been trained to follow the Glenstone approach to gallery assistance: Ask questions to spark discussion, rather than lecture. Spend as much time reading body language as speaking. “They’re taught to know when to back off if someone looks like they really don’t want to have a conversation,” Emily says.

But for visitors seeking more information, Emily wants to make it easy to find a guide. Hence, they wear gray uniforms — just one more example of how nothing is by chance at Glenstone, from the poured concrete ceilings to the ipe wood that lines so many of the museum's walkways.

Those touches are purely Emily, says Aï Bihr, a friend since 1994 when they met in an intro computer science class at Wellesley College. Bihr, a Paris-based designer who helped with the uniforms, says she’s always been amazed at how much Emily can juggle. She is the most completely organized person she knows. “I remember when I was pregnant, and I was like, ‘Can you send me your top 10 products?’ ” says Bihr. “What’s the best diaper? What’s the best milk pump? She had it on a spreadsheet.”

Emily has long, dark hair and an easy laugh, and she isn’t afraid, while sitting with her two young daughters in the kitchen, even in front of a stranger with a notepad, to softly sing a few lines of “Someone to Watch Over Me,” a bedtime favorite of the girls’. During the school year, Mitch drives the children to school and can be at his desk by 8 a.m. In the summer, with camp’s later start time, she hustles them out of the house. There is a clear division of labor during the workday. Emily runs Glenstone. Mitch’s office, with Bloomberg monitors running behind his desk and CNBC on a television within view, is next door to his wife’s. He can always hop into the galleries if a decision needs to be made. “Emily, day-to-day, is really the interface with the artist,” says Roni Horn, one of the living artists collected in great depth by the couple. “Mitch is more in the background on that level.”

Emily Wei was an only child, the daughter of Chinese immigrants who settled in Vancouver. She was a straight-A student, studied ballet and violin, and sang in the school jazz choir. She arrived at Wellesley in the fall of 1994 to major in international relations. She took a modern-art class only because she had space on her schedule. That changed everything.

She would double major in Chinese studies and art history and, before her senior year, land a summer internship at the Guggenheim in New York. Jane DeBevoise, then the museum’s deputy director, put her to work helping with planning for an enormous exhibition of Chinese art meant to stretch from prehistory to the 1980s. Emily, she says, made herself “immediately indispensable.”

It reached the point where DeBevoise didn’t want Emily to return to Wellesley in the fall for her senior year. She asked if she could somehow stay on until “China: 5,000 Years” opened in February. “I was requested to meet her father,” DeBevoise says. “I felt like I was at an interview, and I suppose I was. I passed the interview, but there was one condition — that she live in my house.” Emily, the intern, shared a bathroom with DeBevoise’s 5-year-old triplets on the top floor.

After college, Emily managed a gallery, served as registrar for another and then, starting in 2003, began organizing shows in unoccupied spaces in Lower Manhattan with another curator, Haan Chau. They called themselves Hudson Clearing, placing works by emerging artists without gallery representation in industrial spaces. When she maxed out her credit cards, Emily had to take a job selling contemporary art at another gallery.

Rower, the Calder foundation president and the late artist’s grandson, was impressed with Emily and allowed her to do a show in his building. He had also become friends with Mitch Rales — a divorced older art collector whom he’d been surprised to find so engaging and not a bit arrogant, despite his wealth.

“At one point he turned to me and said, ‘All my friends keep introducing me to this and that guy’s ex-wife and I just want to meet a wonderful person who is not somebody’s ex-wife,’ ” says Rower. “Then on the other side I had my dear friend Emily. She said, ‘If only I could meet a gentleman.’ Do you mean the guy who pulls your chair out if you’re at the dinner table?” He set her up with Mitch.

Emily admits she worried when Mitch popped the question only 10 months after their first date in 2005. Not marriage — a job offer. Leave New York, he said, and come work for me. Hmm. Her mother asked if she was sure about this. So did some of her friends. “I’m a mom, and if my daughter is in her late 20s and she starts dating a billionaire and it’s going well and everything’s great and she then decides to quit her job to live with him and work with him, wouldn’t you feel a little uneasy about the arrangement?” Emily says now. “I’m not the type of woman who was just looking to get married. I’m very serious about work and my career and want to be validated for the work I do, and not dismissed because I’m somebody’s plus-one.”

She thought and thought about it. Emily knew she would be opening up Glenstone’s exhibition hall and also shaping a collection. In the end, “it was just too good an opportunity to pass up.” And if there were any doubts, they were soon answered — by the exhibitions she organized, the publications she edited and the feel of Glenstone. She was clearly a very serious person.

“I’m sure she was worried people wouldn’t think she was,” says Ann Philbin, the director of the Hammer Museum at UCLA. “But she knows her stuff. It’s also clear that she’s the one that’s comfortable front and center in the public eye and speaking about it. She’s so lovely and smart. She has helped him very much come out and articulate what he’s up to. They are a great combination.”

As his collecting partner, Emily has broadened Mitch’s view of art, says David Zwirner, a prominent New York dealer who has worked with the couple. Mitch had started in the early 1990s, primarily buying American masters, including Pollock and Rothko. “She opened up the viewpoint from an international perspective,” Zwirner explains. “German artists, minimalism. And a much younger group of artists that emerged in the ’90s.”

It’s time to hang Rothko’s “No. 9 (White and Black on Wine),” the roughly 9-by-14-foot oil the artist painted in 1958. Mitch acquired it for $16 million two years before he met Emily. But he isn’t about to install it in the new Glenstone without her. They consider how high off the floor to place it. “I would say it’s about 18 inches,” says Mitch, shifting his weight slightly as he hangs back in a doorway.

“He always hangs things two to four inches higher than I would,” says Emily, standing next to him. “Now remember, Rothko always wanted things installed a bit lower so you felt immersed.”

“Want to try 14?” says Mitch.

“I still think it’s pretty high,” says Emily. “I would be comfortable with just 13. Can we just split the difference at 13½?”

The negotiation wraps, and the Raleses head back to the museum offices. She has a staff meeting. He has to take a business call.

They may be separated by two decades and different paths to their partnership, but Emily and Mitch Rales seem very much in sync. As director, she holds staff meetings, attends to the most minute details — how to find the proper shade of red gravel for the Heizer piece or Japanese wood ash for another space — and edits Glenstone’s growing list of publications. He runs his businesses, which besides Danaher include Colfax, an industrial company the brothers founded in 1995. He loves what he does and says he has no plans to give it up.

They are never far from the latest acquisition. They each have The List: a compilation of artworks they’ve already jointly decided they want to pursue if the pieces hit the market. That way, no purchase is made without both agreeing to it.

Their artworks aren’t all they share. The Raleses aren’t shut-ins, but they are not big on the cocktail party circuit. They live with their daughters in the modernist home Charles Gwathmey designed across the lawn from the museum. (Mitch has two adult children from a previous marriage.) Summer vacations are spent at the family home in Maine, not schmoozing in the Hamptons. “I’ve never seen them at an art fair,” says Philbin.

That philosophy is what they’ve always maintained at Glenstone: the idea that it should feel more like a retreat than a glitzy, party-focused Art Basel Miami Beach. And they’re doing this by installing rules and systems and a geographic layout that offers them a sense of control.

Admission is still free, but reservations are required. That will help keep the number of visitors to as many as 500 a day. Parking lots are on the edge of the campus, requiring a short walk through the landscaped grounds to the pavilions. This is meant to connect visitors to the Glenstone vibe as they approach the art. And in this Instagram-obsessed universe, don’t expect to pose near the Pollocks. Cellphones are off-limits in the galleries.

Michael Govan, who grew up in Washington and is now director of the Los Angeles County Museum of Art, appreciates this approach. There are other places that offer enough space to show work you don’t typically find in a major city museum, including Dia:Beacon in New York and the Massachusetts Museum of Contemporary Art in North Adams, Mass. What Govan finds remarkable about the Raleses is their focus on creating a meditative experience at Glenstone. “In an age of instant gratification, desire for publicity, social media, they don’t rush things,” he says. “They spend time. There’s a book that a friend of mine wrote called ‘Slow Art.’ That is the same trend. That there are people that have decided that the world has gotten so complicated in some sense that we need to retreat a little bit and isolate our focus from the noise and operate a little more deeply.”

It’s hard to imagine wanting to rush or wave around a selfie stick as you walk through the new spaces. One room is devoted to the black triptych painted by the late conceptual Japanese artist On Kawara during the Apollo 11 space mission in 1969. The space is bright and the only gallery in the museum pavilions with a wood floor.

Then there’s Gallery 6, a 4,000-square-foot space with no natural light. As we walk through in midsummer, it contains a piece — “Black Pussy,” by the artist Jason Rhoades — that the Raleses are considering for the opening, although they will later decide to hold it and present a video work by Pipilotti Rist, “Ever Is Over All,” instead.

The reason for the change is an important indicator of Glenstone’s transformation to a more public institution. Rhoades completed “Black Pussy” just before his accidental drug overdose in 2006. Two years later, the Raleses saw it in Zwirner’s gallery. “This is one of the few occasions where we didn’t walk into it knowing a lot about the artist, and it wasn’t on the list,” says Emily. “We were just so taken with the work.”

It’s easy to understand why. The piece isn’t so much an artwork as another universe, made up of thousands of objects, from Native American dream catchers to the artist’s own white suit. It’s dreamy, abstract and beautiful. It’s also demanding — specifically the title. A rich collector with a private gallery probably wouldn’t flinch at showing a piece called “Black Pussy.” But a museum with a public to serve has to take a different approach.

Ultimately, the Raleses will realize that the run-up to opening day has left too little time to properly introduce the Rhoades. Among other things, they want to consider whether to present it with a disclaimer for those who might be offended by the title. So the piece will sit for a bit, a tantalizing coming attraction.

But on this midsummer day, as he walks through Gallery 6, Mitch Rales remains in awe. “It’ll take art history another 20 or 30 years to tell us whether this is really a monumentally important piece of art or not,” he says. “We don’t really know for sure. ... In some respects, we have the chance to maybe cast the die on an artist like this by showing the work and keeping it up as a permanent work, as a destinational type of piece.”

Then he asks a series of questions that are specifically about the Rhoades but could just as easily come after a first visit to Glenstone. "There's a lot of people that paint really pretty pictures that I just think are more decorative, nice, but what do they really do that reinvents art? Who does this type of thing? Where the hell did this come from?"

Geoff Edgers is a Washington Post staff writer.