In early period, gold wire was availible for decorative uses (eg brocaded tablet weaving). By about the 12th Century, threads where very fine gold was spun about a core of silk (or occasionally linen) were availible. These looked to the naked eye much like a solid gold wire, but could be used more like an embroidery thread (more flexible). Such threads could be used in embroidery, more intricate brocaded tablet weaving, and also to weave gold cloth.
Some modern threads made using synthetic cores are actually quite good mimics of these period gold threads, which could be spun extremely fine.
Silver can be used in the same way, and was during the medieval period, but it tarnishes quickly, making it less desireable.