On the eve of the opening of his retrospective, “Stephen Jones, Chapeaux d’Artiste,” at the Palais Galliera, in Paris’s Eighth Arrondissement, the famed British milliner is fitting a lacquered straw boater on the head of a friend. Because this natty number is by Jones, it bears only a passing resemblance to traditional headgear of its genre. Its scale is reduced, its color is oxblood, and its low crown looks like a lambchop, finished with a frill.

As the designer is pressed for time, he has made a corner of Les Lounges, on the ground floor of the princely Shangri-La hotel, into a posh makeshift atelier. Other hotel guests, scattered on tufted banquettes and silky divans, pause their conversations to watch a metamorphosis take place before their eyes. Jones nimbly tilts the hat a few degrees, rotates it into place, and walks his friend to the room’s mantel mirror. She has been transformed—her facial structure has sharpened, her irises have brightened, and her whole countenance has assumed an enigmatic allure. Acknowledging the effect of his handiwork, Jones says, “It’s magic.”