Just when you thought the past might be vanishing a little too quickly, terra cotta is coming back in new ways, making New York warmer, deeper, and not so flat and icy with glass.

Midnight-blue glazed terra cotta, all full of inky depth, will surround the lower portion of architect Annabelle Selldorf’s 520 West Chelsea condominium building on 19th Street. At Ms. Selldorf’s 200 11th Avenue, where people will drive their cars into their apartments, cast gunmetal glazed terra cotta is to cover the base, making curves and warmth in a cold, sharp world.

The upcoming Museum of Arts and Design (M.A.D.) building—the former “Lollipop Building” at 2 Columbus Circle—will reportedly be faced with lustrous, iridescent terra cotta along with the glass, though the building is enshrouded now and no one is quite sure what is going on underneath. Terra cotta hasn’t been in fashion since the 1930’s, when the Great Depression stopped construction and modernism subsequently brought in more machine-age textures.

And the days of flurries of terra-cotta leaves and grapes are probably gone: no more ruffled flounces, no more cupcake look or theatrical flourishes. Terra cotta always had a stagy quality, partly because one sees it applied in pieces since it is baked in parts, in kilns. So there is always the sense that terra cotta is pretending to be a big surface. There is the charm of the clay, the touch of the hand pulling it out of the mold. Look inside old pieces and one sees thumbprints.

Today, you wouldn’t recognize it. Terra cotta looks entirely modern, its cheeks pulled in, as if it has been going to a gym, all flat, perfect little blocks or rectangles. These are shapes comfortable to the modern age, a celebration of the uncluttered yet ornamental in its textural effect. For no matter how modern we all are, we will doodle a bit.

Sara Lopergolo, a partner at Ms. Selldorf’s firm, said that they chose terra cotta not only because a lot of the city “was built with that material on the exterior,” but because “the material, the color has a depth you just don’t see any more.” And, she added, “it picks up light once it’s curved …. All the architects are excited the way the terra-cotta glaze reflects light, and especially that of glass around it.”

Terra cotta means “burnt earth”; it is essentially fired clay. There is something volcanic in the way the shapes are stopped in motion, a bit like photography, that second in existence held right there, a dramatic hold-your-breath moment, forever stopped in motion, lava about to overwhelm—then it’s held back by fire and cooked. Not at all like stone, which looks exactly what it sounds like, a more graveyard sort of thing.

Terra cotta has its own organization, the Friends of Terra Cotta. Do they sit about staring at pediments with terra-cotta seashells in each other’s living rooms? “Polishing terra cotta with our shirtsleeves?” said Simeon Bankoff, executive director of the Historic Districts Council. “No. We get newsletters. We have chapters. We do not ‘take it for granite.’” Mr. Bankoff was referring to the second half of the title of one of Friends president Susan Tunick’s many terra-cotta books. Ms. Tunick quotes a 1911 New York Times article describing the city’s skyline as “more than half architectural terra cotta.”

Building façades were cheerfully ornamented with its natural clay color or glazed in yellow, green, blue, silver and gold. Even on the darkest days, tenement buildings had masonry façades full of ruffled glory. So many of New York’s boldface names have it: the Flatiron, the Woolworth, Louis Sullivan’s Bayard-Condict on Bleecker, Judson Memorial Church, and the Fred French building with madly colored beehives, griffins and a rising sun. A favorite is the green terra-cotta trim on the First Presbyterian Church chapter house at 12 West 12th Street, which always seemed to be a mysterious building in a Chinese garden, though it’s not Chinese at all. It was built in the late 1950’s by a Frank Lloyd Wright disciple, thus the horizontalness, but the particular shade of terra-cotta green makes it almost like jade.

Terra cotta was a little hero that could do no wrong. Its ornamental and fireproofing qualities and increased availability led to its use from the 1880’s through the 1920’s on building façades, rooflines and lobbies—and of course, inside Grand Central Terminal. Terra cotta was cheaper than stone. According to Ms. Tunick’s entry in The New York City Encyclopedia, after James Renwick in the 19th century engaged a sewer-pipe factory to manufacture cornices and window surrounds as a cheaper substitute for cut stone, stone cutters and masons got upset that terra cotta would endanger their livelihood. They helped keep it out of the city for years. The terra-cotta wars, one might say!

That was then.

The other day, architect John Cetra calmly stood in his 584 Broadway office stroking a 110-year-old scrolled pediment that had framed a brownstone on East 66th Street. “There is a depth to the material you don’t see in stone,” he said. “We just love the look of it. Look at those fissures. Of course, that comes from water that is trapped inside. New systems are using terra cotta very differently—it’s being designed so water will not be trapped.” Mr. Cetra and his wife and partner, Nancy Ruddy, recently used red terra cotta from Germany on the sides and at the setbacks of the glass-curtain wall of the Ariel East at 2628 Broadway. “We incorporated it into the glass,” he said. “It becomes a tracery to give the building some distinction, but also to relate it to the Metro Theater to the west.” Cetra/Ruddy also did a condominium conversion of the turn-of-the-century 141 Fifth Avenue, which has terra cotta on the cornice, over the entrance, everywhere. Developers believe people will pay more to live within the confines of madly swirling and curling terra cotta. Though 141 Fifth Avenue’s Core Group Marketing C.E.O., Shaun Osher, will never forget the penthouse of the Police Building on Centre Street that he sold with the 35-foot terra-cotta ceiling. “The woman covered it up,” he said.