"Hopi silver jewelry has been crafted over a period of 100 plus years, beginning just before 1900 and continuing today. By the mid-1930's some of the silversmiths had begun to mark their jewelry with a personal stamp referred to as a silvermark, but is commonly called a hallmark by collectors.
Mary-Russell Ferrell Colton in the late 1930's sought to encourage Hopi silversmiths. She stated "There is only one way to make Hopi silversmithing worthwhile, it must be different from any other Indian silversmithing. They must produce Hopi silver, not Navajo, Pueblo, or Zuni. . . using only Hopi design.
Overlay, as used in Hopi silverwork, is basically a piece of silver with a design cut out of it--a negative design. . . The silver that is left after the design has been cut out of it is the part used. This piece is soldered onto a sheet of plain silver and the inside of the design oxidized to show up black against the polished silver." Hopi Silver The History and Hallmarks of Hopi Silversmithing by Margaret Nickelson Wright