The painting gallery at The Glass House compound in New Canaan dates from 1965 when the architect and culture titan Philip Johnson had it built to house the growing art collection he shared with his much younger partner, David Whitney.

Its design, like the iconic Glass House itself and most of the property, is rigorously geometric. Windowless and covered in earth, the gallery’s open interior is shaped as simply as an old-fashioned keyhole: a rectangular foyer leads to a circular inner chamber.

Typically for exhibitions, the foyer can function as gateway or prelude to the big show further inside, where Johnson dictated that no more than six paintings should be shown at any one time. For this summer’s big exhibit, however, the foyer is essential viewing.

Titled “Personal Effect: Works from the Collection of Philip Johnson and David Whitney,” it includes art from Warhol, Rauschenberg, Stella, Salle and Johns. Most have never been shown before. And while some are only untitled sketches, done on scraps of paper, they all have outsized importance to telling the story of the exhibit, which is of Johnson and Whitney and their world.

Moving around the foyer, Hilary Lewis, who last year was named chief curator and creative director at The Glass House, points out example after example.

Here is an untitled oil painting by Jasper Johns, a sliver only three inches high, done in such dense, dark hues that its engraved image can barely be discerned. Lewis leans close to it and reads, “For David, March 28, 1967.”

Even though the painting was done four years later, she presumes the date refers to Whitney’s birthday, March 28. Standing back, she adds, “For those who don’t know the work of Jasper Johns, that’s quite a painting.”

Nearby is a colored sketch of eight fanciful buildings the post-modern architect Michael Graves did for Johnson’s 80th birthday, in 1986. On the opposite wall is another 80th birthday year gift, this one from Frank Stella, a three-dimensional model for a sculpture fashioned from foam and looking like something from an abstract pop-up book.

Stella was a friend and one the artists most heavily represented in The Glass House collection. Lewis says Da Monsta, a structure Johnson added to the property in 1995, was so influenced by Stella’s design for a museum in Dresden, Germany, that he sometimes called it Dresden Two.

The foyer contains some of the most personal pieces from the collection, Lewis says. “They are smaller in scale, yet when you see the artists involved, they are some of the biggest names in American art and architecture.”

There is one notable exception, at least in terms of nationality. Also in the foyer are two small pencil sketches of simple geometric shapes that appear to drawn on brown-bag paper. But they are by the long-dead Russian artist Kazimir Malevich, whose radical theories about color and shape are said to have influenced the evolution of modern art. More personally, Malevich’s geometry probably influenced the design of a garden kept by Whitney and also Johnson’s own conception for the glass house.

“I found those in storage and said, ‘My goodness. We have two Maleviches. We have to show them,’ ” Lewis says.

Lewis is a Johnson scholar. She first met him as a graduate student in 1992 and collaborated with him on several books. She says the germ of her idea for the new exhibit came from one of the six large paintings on display in the inner chamber: Andy Warhol’s nine-panel portrait of Johnson done in 1972.

The silk-screen painting has never been loaned, nor even seen in full view since The Glass House property was opened to the public in 2007 under the auspices of the National Trust for Historic Preservation. Johnson had designed the painting gallery with movable panels he could shift to reveal different paintings.

“Sometimes we had one of the panels tilted a bit so you could glance in and see the Warhol,” Lewis says. “It was a desire of mine to see that work straight on. I worked with Philip Johnson. I know he liked the panels flush.”

Among the other five works sharing the space with Warhol are two eight-foot tall mixed media giants by David Salle and Robert Rauschenberg (his has a working fan) and a sort of architectural sketch run wild by Michael Heizer, a pioneer in earth sculpture. The 11-foot wide piece once hung in Johnson’s New York office. Its abbreviated title, “Dragged Mass,” refers to an early Heizer outdoor project: a 300-ton dirt mound created by dragging a 30-ton block of granite back and forth.

The final two pieces are large linear grids by Stella again. One titled “Averroes” is done in aluminum paint on a notched canvas. Lewis says it is too delicate to loan and is probably the most valuable piece in the collection. It is also the first that Whitney advised Johnson to buy. Acquired in 1961, it was painted in 1960.

That was the year Whitney and Johnson met. After listening to Johnson lecture at Brown University, Whitney, then an undergraduate at the Rhode Island School of Design, introduced himself and asked to visit The Glass House. It would be several years before he moved in. Despite the three-decade difference in their ages, they died months apart in 2005.

The “Personal Effect” exhibit runs until Aug. 12. Access to the painting gallery depends the kind of tour booked.

Joel Lang is a frequent contributor to Sunday Arts & Style.