For a true primitive string for a replica or rendezvous, I think sinew, gut, or rawhide are the way to go-it's what was on the vast majority of Native American bows. Very few old bows have plant-fiber strings on them. I wouldn't consider linen to be a primitive string material unless you grow the flax and process/cord it yourself. If I'm gonna buy something on a spool from a factory, it'll be dacron or FF. I use B-50 dacron for most of my strings. Artificial sinew is just waxed nylon string, and it's very stretchy. I've made a few strings from it, but dacron is much better IMO. Strings are easy to make once you initially get it figured out. You don't need all the jigs and stuff to make Flemish strings, either. I like a Flemish string with a braided loop at one end and a timber hitch at the other.