This 19th century English-made 60" guard chain was fashioned with niello, a dark metallic alloy of sulfur with silver and/or copper that's used to fill in etches and grooves in metal (typically silver). Sometimes misnamed "black enamel," niello technique spread throughout Europe during the late Iron Age and is common in Anglo-Saxon, Celtic, and other types of Early Medieval jewelry. In this piece, grooves were created in the necklace's long links, these indentations were then filled with the black-toned material. Gold links alternate with the niello and silver to create a fantastic three-tone effect.