I had the pleasure of meeting Carol James, språng artist, teacher, and author of Sprang Unsprung. She gave a public talk and displayed many of her finished objects.
If you read the paper she presented to the Textile Society of America in September, 2012, "Re-creating Military Sashes: Reviving the Sprang Technique," http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1697&context=tsaconf, you will get some of the same content as the presentation I attended. There is some information in the paper about how the yarn was traditionally spun, on spindles and not plied.
I got to see her replica of the Braddock sash.* The full-scale replica is enormous and done in very fine silk. Laid out, it took up the top of an entire banquet-style folding table.
I liked sitting at an angle opposite the window and seeing the way the light struck the surface of the sash because I could really see the difference between the cloth on one side of the meeting line compared to the other. Even though the yarn was all dyed evenly in madder and over-dyed with cochineal, the difference in cloth structure caused one part to look darker than the other. The sash was worked in one piece in a circular warp, so all of the interlinking on one side of the meeting line, that is, one half of the sash, had small twists of threads all over its surface twisted in the Z (clockwise) direction and the other was twisted in mirror image. That's why the light struck them differently.
There were patterns of holes, including some in the shapes of identical men standing in a row and some in the shapes of small triangles.
You can read about the original sash here on the Mount Vernon site. The Mount Vernon Ladies' Association now has Carol James' replica sash in their collection as well.
There was a fair amount of collaboration that went into the project. She had friends (and I think I remember family as well) assist her with warping and they must have borne her a lot of good will, as she said it took five hours to complete that step. She advocates seeking grant funding for fibre arts work. It was interesting to hear her speak of the Association's position on copyright, the limited license they gave her, and the conditions under which she got access to the sash and by extension the information about thread size, pattern design and placement, dimensions, dye shade, and so on. We were asked not to take photographs of the sash because the Association has copyright. To hold something like that in a collection is certainly valuable, and so is access.
*The original sash had the distinction of being owned by George Washington, the first president of the United States. I gather that one of the reasons people regarded Washington highly was his military leadership as commander of the Continental Army during the American revolution. Before that, he was a member of the British forces in the French and Indian War, where General Braddock gave him the military sash and the command that went with it.