Cyndy left a comment with a question on my last post, and since the answer was going to make for a very long return comment and I wanted to ask a couple of questions of my own, I'm cheating and posting it instead. :-)
I had actually thought of Navajo-plying the remaining singles, but I'd never done it before and decided to test it first. So, I pulled the merino-silk off the wheel and spun up some plain wool in fingering-weight singles, then tried to chain ply them. I cannot tell you what a mess I made. Well, ok, I could, but it defies description. :-) I think the problem was that I had too much twist in the singles (thinking it would work the same as a standard 3-ply), and then overspan the ply. It didn't help matters that the "knots" really showed; it was impossibly ugly. I realized pretty quickly that if I couldn't manage it with some vanilla wool at a much heavier gauge, I'd never make it with very thin laceweight singles (assuming the suckers didn't break in the process).
I even thought about rearranging the singles into a center-pull ball and one single, but center-pull with high-twist thread gets nasty quickly, I'd still have a bit of single left over, and I wasn't sure it would be worth the work just for a couple yards of finished yarn. The leftovers aren't lost; I'll save them for something later, or use them for yarn label tags.
I DO, however, need to figure this out. I pulled out some black-white roving from The Sheep Shed Studio to experiment with, and started spinning a fingering-weight single last night. I'll give myself a couple of ounces worth and then try my hand at chain plying it again. This time, though, there's considerably less twist in the single, so we'll see what happens.
But there must be a way to use all the singles in a plain three-ply? Obviously equalizing weight per bobbin would help, but what if you're not spinning a perfectly consistent single? (I'm working on it, but I'm not there yet.) You'll still end up with more on one than another. And what about the "bump" or knotty spot in a Navajo ply? How does that join affect the wear of the yarn? In other words, are there some purposes for which a Navajo-plied yarn would be less "good" or effective than others? I wouldn't think it would make a difference for scarves and shawls, but how does it do for sweaters or clothing?
See? All I have are questions these days. :-)