As several have already suggested, it perhaps is not that important what you string them on, though I would not use metal threads, as pearls are simply too soft a gem and you will end up doing damage to your pearls as zeide said. We have experimented with a few different natural fibers including a "mo-hair" (have no idea how it is spelled) and we actually prefer it best for its durability as well as how nicely the pealrs lay. However, we have not switched over as there is still a perception that silk-based products are best, so that is what we continue to use.