In late March, I visited La Paloma’s vast workshop on the fringe of the San Fernando Valley. Ron and his team, now led by his son, Edan, have installed every “Chocolate Room” but the first: “Los Angeles twice, Palm Springs, Anchorage, Reno, Oklahoma City.” The New York install is different. Ruscha’s survey is an occasion to dial in the “Chocolate Room” recipe for the ages.

To get the shingles to hang straight, they chose a coated paper. They experimented with different chocolates, too. “We wanted to stick with a commercial mix,” Edan said. “Something you could get consistently.”

They’d always used regular Hershey’s bars before. So long as the brand uses pure ingredients, it’s a matter of color. They’d winnowed it to three — Hershey’s regular, a dark Ghirardelli’s and a darker Callebaut — and sent samples to Ruscha’s studio. He chose the Callebaut. MoMA’s team matched it with a touch-up paint, to fill in around the walls’ edges: Benjamin Moore Arroyo Red.

Most of all, La Paloma wanted to prevent the powdery, fatty bloom that sometimes, not always, covers the chocolate’s surface. The trick, as chocolatiers know, is to temper the chocolate, and keep it tempered as it’s shaped.

The double boilers they’d been using to melt the Hershey’s bars were inexact. Now they travel with the ChocoVision Revolation Delta, an electronically regulated, air-heated, self-stirring metal bowl that puts chocolate through its paces, up to 115 degrees or so, then back down to 86. Then, explained Edan, “you add a little bit of unmelted chocolate, and that tempers it.” It’s called “seeding”: “The seeding tells the cocoa butter molecules how to realign correctly inside the chocolate.”