When Nicole Giessman was decorating her new master bathroom, she ordered two oval mirrors lined with mud starfish and scallop, abalone and pearlized turbo shells. "It’s probably the first time I’ve used a seashell motif," she said. "A lot of the things I’ve seen out there are a little overdone, but I liked the simplicity of this one."

Seashells, corals and starfish used to be the kind of things primarily sold in seaside tourist shops, but lately they’ve been showing up more in mainstream design, incorporated into furniture or as stand-alone art pieces costing as much as $1,000. Ms. Giessman bought her $99 mirror from Harvest of Barnstable, a Cape Cod, Mass., retailer and wholesaler that makes shell based decorative objects. After one of its designs appeared in a shopping magazine, the company received 40 orders in two weeks.

From Renaissance to Rococo

In spite of their recent-and somewhat tacky-past, seashells used to be a key accent to a stylish, elegant and wealthy household long ago. Their use dates to the Renaissance, when garden grottoes were fashionable, explained Daniella Ohad-Smith, who teaches design history at Parsons School of Design in New York. These cave-like structures were decorated with moss-covered rocks, shells and other marine life. "It was the most luxurious garden feature of the wealthiest and most cultured Renaissance people," Ms. Ohad-Smith said. Shell motifs influenced the 18th-century French decorative style known as rococo, derived from the words rocaille and coquille (rock and shell), and later Art Nouveau, which brought together nature and art, incorporating shells into bronze or glass objects.