“You need a Joseph Cornell box over your fireplace,” my friend Jerry said after we’d drifted through the artist’s exhibit, “Navigating the Imagination,” at the San Francisco Museum of Modern Art.

Why, yes. Of course. And they look so easy, the shadow boxes framing arrangements of everything from clay pipes to photos of birds to watch faces to restaurant menus.

But Cornell, who practically invented an art form from the basement of his house in Queens, New York, was a genius. (The street he lived on, by the way, was Utopia Parkway.)

Cornell was born in 1903 and scoured New York City for his material and inspiration, which he collected in boxes with such labels as “Glasses” and “Durer” and “Tinfoil” and “Sea Shells.”

He reflected a number of trends from the early part of the 20th century, but he was 64 years old before he finally received major recognition in the art world.

There’s nothing precious about Cornell’s collages and boxes — they’re not cute craft projects from a magazine. He hasn’t simply cleared off a workroom table, as we might, and arranged the items in a frame.

Everything means something to him, even if it’s a mystery to us. Inspecting the 170 works in the galleries at the Museum of Modern Art is like searching for clues to American life.

A quote from one of Cornell’s favorite literary works, Walt Whitman’s “Leaves of Grass,” introduces the exhibit and marks the route: “Now, Voyager, sail thou forth to seek and find.”

Buying a Joseph Cornell box to put over my fireplace would cost tens of thousands of dollars. Reproducing one would miss the point — that every detail of his work is deeply personal.

Maybe I’ve already got a good start, even if it’s spread out, not in a box.

There’s a 19th century clock decorated with a frieze of some classical battle to which I’ve added, on a ledge, a tiny figure of a middle-aged shopper from an architectural model. There are drawings of temples in Kyoto by San Francisco architect Ira Kurlander, and Arts and Crafts bowls discovered on trips to Massachusetts and Vermont. There’s a postcard photo of the original “butterfly chair” designed in 1938.

There are also three small collages made from 19th century newspaper clippings and illustrations and vintage wallpaper borders made by my friend Robert Warner, a former Oakland resident who’s now an artist in New York. Maybe I’ll leave things as they are — after all, it was Warner who introduced me to the magic and mystery of Joseph Cornell in the first place.