Curtains, however pretty, have a largely utilitarian purpose: to control light and soften the architecture of a window. For 20th-century style icon Pauline de Rothschild (1908-76)—an American fashion designer turned hostess of one of France’s greatest wine châteaus—the design of a curtain could, believe it or not, be an artistic and intellectual challenge, where inspiration intersected with erudition and resulted in a window treatment that could embody as many layers of meaning as it employed layers of fabric.

The confection made for the London apartment that Pauline and her vintner-poet husband, Baron Philippe de Rothschild, owned from 1970 until her death in 1976 is the best-known example of her creative approach to curtains. As seen in the May/June 1977 issue of Architectural Digest, the floor-to-ceiling bay window in the double-height drawing room—the grandest space of the four-room residence at Albany, a famously exclusive, 19th-century redbrick complex in Piccadilly—was dressed in so memorably eccentric a fashion that it seems difficult to believe the curtains were produced under the watchful eye of interior designer John Fowler of Sibyl Colefax & John Fowler. His specialty, window-wise, was tassels and swags, and his decorative style was an inviting spin on classic English country-house elegance. Rothschild, on the other hand, possessed a sui generis aesthetic sense heralded by Vogue as “le style Pauline,” so when it came to the decoration of the apartment (a “set” in Albany parlance), the division of labor was crystal clear. The willowy baroness, then in her early 60s, would serve as creator, while Fowler and his assistant, Imogen Taylor, now a grande-dame designer herself, ensured that their client’s often startling ideas about decor became reality.

“Pauline had the mind of a mosaicist,” said Stuart Preston, the late New York Times art critic, when I visited him in Paris years ago. It was an insightful observation that proved to be the key to le style Pauline, and one later bolstered by my discovery of an unpublished manuscript written in the 1950s by photographer Cecil Beaton, in which he described her New York City townhouse as “a record of impressions alluded to, but not stressed, a remembrance of beauty rather than beauty itself.”

From her days as a designer at the renowned New York fashion house of Hattie Carnegie through her marriage to Philippe, the former Pauline Fairfax Potter magpied details from a wide range of sources—a painting, a book, a memory, a long-ago conversation—and then deployed them like a tile setter manipulating tesserae, carefully incorporating them into a dress she was designing, a room she was decorating, a dining table she was setting, the flowers she was arranging. Thus her admired creations come equipped with invisible footnotes that make them much more than what meets the eye.

Fashioned by London upholsterer Peter Atkins, the Albany window treatment is the best-known example of Rothschild’s idiosyncratic and intensely personal taste. For instance, the two layers of unlined oyster-colored glazed chintz that make up the deep valance have their edges cut into dramatic zigzags that would flutter slightly in every passing breeze. (The same crisp chintz is used for the inconspicuous draw curtains that provide privacy.) Though it appears to be a frisky alternative to the usual window dressing, that scissored detail evokes specific moments in Rothschild’s life—her cherished winter trips to the Soviet Union, where she marveled at the icicle-fringed windowsills of Saint Petersburg’s candied-colored baroque palaces.

As for the decorative dress curtains composing the window treatment’s outer layer, they are marvels of the upholsterer’s art, cataracts of citron silk taffeta at least 20 feet long, pouring down from the dentil cornice, past Ionic pilasters painted to look like lapis lazuli, and onto the marbleized parquet floor, where the shimmering panels fan out like the trains of belle epoque gowns. The baroness, Atkins once told me, called them “Madame Geoffrin curtains, though I don’t know why.”

The answer to that puzzlement I found in a 1773-74 Hubert Robert painting of the Paris bedchamber of Marie-Thérèse Geoffrin, the Enlightenment salonnière and arts patron, who happened to be one of Rothschild’s spiritual idols. In that work each of the full-length curtains, which flank a pair of French doors and also the adjacent alcove housing Geoffrin’s bed, are gathered with tasseled cords into four long puffs. Rothschild copied the look almost exactly for the oval salon of her apartment in Paris’s 14th arrondissement, though in London’s Piccadilly she personalized the design. There the puffs were deflated and straightened out, and the discreet cords were eliminated in favor of large double bows mounted onto wide ruched bands; smaller bows terminated the ruched pulls that raised and lowered the bay’s three vast double-hung windows.

Two obscure inspirations equal one window treatment that remains a cut above the rest.