Seaman Schepps’ signature turbo shell earrings rank alongside Verdura’s 1930s Maltese cuff and Jean Schlumberger’s 1960s enamel bangle as one of a handful of iconic 20th-century jewelry designs.

Many craft-based small businesses begin with a plentiful raw ingredient and creativity -- like seashell crafting. Entrepreneurs with ample access to a good source of shells, like a public beach, have ...