Middle Eastern Niello Clasps

Niello is a centuries-old metal-decorating craft most often seen on a silver base, though it was also used on copper-alloy metals such as brass or bronze. In Middle Eastern, Caucasian, Russian, and European decorative arts, niello was used on jewelry, boxes, weapons, religious objects, and dress accessories.

The design is first engraved or recessed into the surface, then filled with a black metallic sulfide mixture that may contain silver, copper, or lead. Once fused and polished, the dark material remains in the lines of the design, creating the dramatic black-and-silver contrast associated with niello work. For button collectors, its appeal lies in those delicate dark patterns—scrolls, florals, borders, and tiny scenes that look almost drawn in ink, yet are permanently bonded to the metal.

Wikipedia: Niello