A couple of people have commented on my comments about choosing a thread for the background of the Elizabethan pincushion - so here goes.
My research shows that it was a metal thread used for the background whether it was tent or straight gobelin or encrouching gobelin. The comments from people who have received training at the Royal School suggested 371 (gold) for doing plaited braid stitches and something finer for background stitches. 340 (gold) and 345 (silver) are finer and supposedly about the correct diameter for the stitching. 371 is too stiff for stitching, but that is what makes it good for doing the braided stitches. 340/345 would probably work for an encrouching gobelin stitch because of the layering of the thread would create sufficient coverage. It didn't work for straight gobelin on 36 count linen.
The swete bags historically were anywhere from 28 to 42 count; versus slips in wool around 25 count. I chose 36 count because single thread of silk in tent covers nicely.
So back to the search for the best metal thread. Passing was the right diameter but like the 371 it was too stiff. The Indian version of 345 was also too fine. I tried the silver DMC floss which provided better coverage, but still not sufficient. It probably would be useable if you used an additional thread - 4 instead of the normal 3 twist. The Kreinik very fine braid worked to cover adequately. It isn't real metal thread, but it got the job done and has the right look.