Art Nouveau design had a brief but important popularity from 1895 to 1905. L'Art Nouveau was introduced in Paris and spread like wildfire. Several U.S, companies leaped on the bandwagon, among them the Newark, N.J. Unger Bros. The company made pocket knives and specialty hardware starting in 1878. In 1880, a new designer joined the company and silver Art Nouveau jewelry was added. They became famous--and collectible! Their designs were largely die-stamped pieces that have the look of repousse work. Art Nouveau began to lose popularity and the company retired this jewelry in 1910. By 1915, the style was no longer popular.
The maker's mark for Unger Bros was interlaced initials plus 925 sterling stamped on each piece.
[References: Warman's Jewelry, Christie Romero, 2002 American Jewelry Manufacturers, Dorothy Rainwater, 1988]