It’s a power earned through lots of creative work behind the scenes. Special exhibition items represent the enterprise of the museum’s own merchandising and marketing wizards, who aim to translate high art into saleable mementos. For “Art and Love in Renaissance Italy,” opening November 18 at the Met, the exhibition curator Andrea Bayer and the product-development team met several times to discuss marriage and courtship during this era. “[Bayer] talked about the dowry for the bride, the use of quotations in some of the art and the key works and themes in the exhibition,” says Valerie Troyansky, a nearly 30-year veteran of the Met, who oversees product development there. Troyansky’s corps of some 45 developers, buyers and production staff spent more than a year creating objects that relate to the show, which includes paintings and drawings of amorous subjects and celebratory items for weddings and pregnancies, ranging from wedding rings to birth trays.

The result: a mix of jewelry (a locket, a silver pendant and a bracelet incorporating quotations from the period); textiles (velvet scarves, lacework and pillows); and items for the home (picture frames and a majolica pitcher) that capture the traditions and romance of Renaissance Italy. Producing some items required both scholarship and trend savvy, like selecting a fragrance from Santa Maria Novella, the Florentine perfume manufacturer founded in 1621, that would appeal to contemporary women while still being redolent of that storied age.

When Stuart Gerstein, the Philadelphia Museum of Art’s director of wholesale and retail operations, is not consulting with curators about exhibition images and motifs or discussing packaging and marketing, he is attending gift, fashion and accessory trade shows—up to 10 a year—in search of outside products pertinent to upcoming shows. “I’ll be walking through with this idea of, say, Renoir and the French landscape, and I’m looking for things that I think can support that theme,” he says. It was at a fashion-accessory show that he ran into a hatmaker who suggested velvet chapeaus with floral appliqués for “Renoir Landscapes.” During the exhibition’s three-month run, the museum sold 760 of them, priced at $48, and felt berets, at $40 a piece.

Jewelry is the Met’s largest retail area, representing about 25 percent of total sales, says David Wargo, the museum’s general merchandise manager. The business began in 1877, when it contracted with Tiffany & Co. to manufacture and sell copies of Cypriot jewelry in its collection.

For its Frida Kahlo survey this past spring, the Philadelphia Museum of Art enlisted a jeweler to make an elaborate sterling-silver necklace like the one the artist wears in her 1940 Self-Portrait with Thorn Necklace and Hummingbird. The price: $4,375. Among the other Kahlo merchandise were embroidered wool jackets, hand-painted wood bowls and paper flowers from Mexico fashioned from cornstalks. “The store was blue, like Frida’s house,” says Gerstein, who traveled to Mexico City to see her work and to negotiate licensing rights.

Not all shows have the luxury of a dedicated gift store, but all retail display space in a museum is valuable real estate. Wargo says that the Met’s targets for gross sales range from $50,000 for a “very tiny” exhibition, with just a stand of books, to more than $1 million for a blockbuster show, such as the van Gogh drawings in 2005. The profit from publications and reproductions for the 1997–98 “Treasures of Tutankhamun” amounted to more than $8 million, a sizable percentage of which was from the sale of 3-D merchandise across the U.S. It’s no wonder that the Met’s on-site retail operation has ballooned from a modest Information and Sales desk in 1910 to the present 12,500- square-foot main store plus bookstands and smaller shops scattered throughout the building.

Today, artists are often enlisted to design items for their museum shows. Calnek’s favorites from his time at the Guggenheim include the sweatshirts, stickers and motorcycle-jacket patches created by Matthew Barney for his “Cremaster Cycle” retrospective in 2003. “He had a whole studio to make costumes, logos and scenery for the films that were easily turned to merchandise,” Calnek recalls. “We let his studio loose on that.”