This is the delicate craftsmanship of soldering threads of gold and silver in intricate patterns onto jewellery. See: Encyclopaedia Britannica. Sometimes this can also be granulated strands. The technique has been around since ancient times and throughout the Viking Age, too, especially in Ireland and England among the Celts, Briton and Saxons. (See: Shannon L. Venable, Gold: A Cultural Encyclopedia (Santa Barbara: ABC-CLIO, 2011), pp. 109 and the blog Viking Metal.