When they met, Herb already had a small art collection; he had spent his savings on a Picasso lithograph that he says was "more expensive than anything I’ve collected since." Dorothy also had the collector’s bug, but she accumulated postcards, shopping bags and bookmarks. The first artwork they bought together was a small metal sculpture by John Chamberlain that resembled a crushed toy car. Soon there was no space left on the walls for their own amateur efforts, and they decided to devote themselves to collecting.

Everything they owned became a piece of a larger, never-completed jigsaw puzzle. Their preference was for work that was austere and uncompromising. However, their tastes were also molded by practicality. Pop art, then in vogue, was too expensive. "The only thing we could afford was Conceptual or Minimal," Dorothy says, "and we had very few competitors." It seems paradoxical that a couple so at home in all this clutter should be attracted to Minimalism and Conceptualism, art stripped down to its most fundamental features. Herb says that they had two simple rules: "It had to be affordable, and it had to fit into the apartment."

Did the Vogels ever argue about the works they chose? "He was better at collecting works by Lynda Benglis, who is more flamboyant," Dorothy says. "And I seem to have been better at selecting more cerebral works. But he liked what I chose, and I liked what he chose. We rarely had arguments about anything."

A guided tour of their apartment reveals that even the Vogels’ bathroom is replete with artwork. On one wall is Sol LeWitt’s Wall Drawing #65, 1971, a mural completed by Dorothy according to the artist’s elaborate instructions. Opposite the bathroom is a text piece by Lawrence Weiner commenting on the Vogels’ collection: "MANY THINGS PLACED HERE AND THERE/TO FORM A PLACE CAPABLE OF SHELTERING/MANY THINGS PUT HERE AND THERE."

In their collecting heyday, the Vogels spent almost every night at gallery openings discovering new work. They bought straight from the downtown studios of the little-known and impoverished artists who populated SoHo and Tribeca. LeWitt was a big influence on their choices. They met him at the legendary Leo Castelli gallery in 1965 and became fast friends. Until LeWitt died, in 2007, he and Herb spoke by phone every Saturday morning. "We looked up to him not only as an artist but as a collector," Herb says sadly, "and we followed a lot of his ideas."

In Herb and Dorothy, an intimate new documentary about the Vogels by the Japanese filmmaker Megumi Sasaki that is being released June 5, Chuck Close describes the tiny couple as "the mascots of the art world," and he says that artists would offer them knockdown prices "because they were cute and funny and passionate and enthusiastic when no one was interested in what we were doing, but also because they came cash in hand."

A drawing by Will Barnett, whose work the Vogels have collected extensively, depicts the couple looking at an artwork. Herb is shown bending over a canvas, as if sniffing the wet paint. "He points at the art like a hound," the artist Lucio Pozzi has said. "He’s like one of those dogs that digs for truffles, and his eyes become intense." Dorothy would often leave the room while Herb bargained. They refuse to discuss the prices that they paid but acknowledge that "the collection is built upon the generosity of artists." Because of their financial constraints, much of what they own is drawings or preparatory gestures, and as a result the collection, unlike those composed of trophies, illuminates its participating artists’ working methods and offers a history of art behind the scenes.

Christo and his working partner–wife, Jeanne-Claude, remember getting a call from the Vogels and thinking, "Hooray, we’re going to pay the rent!" But when Herb and Dorothy heard the artists’ prices they sighed, "Oh, my God, we came too late." The artists, however, were flattered by the couple’s seriousness and asked the animal-loving Vogels to look after their cat when they left for Colorado to build their monumental Valley Curtain. In exchange, the artists gave the collectors a preparatory collage of the orange dam, the first of many works the Vogels now own by the Christos. The two couples became friends, as the Vogels did with many of the artists they admired. "They treated us like we were artists," Dorothy says of the people they collected. "I think we shared the same sensibility, feeling and approach to art." The artist James Siena describes them as "more like curators than collectors."