When I began spinning, I had a very limited supply of bobbins, and a very limited budget. My first skeins were plied from singles that were balled and placed into canning jars. I had read about Navajo plying, but most of what I had read was somewhat belittling to the technique, often referring to it as something only done while spinning in public to get the attention of passersby. As time went on, I found that not only was Navajo plying useful, it was essential.
When you think about what makes a good yarn, there are a few things that automatically come to mind. In most cases three ply is better than two ply in that there is more strength in the yarn. It can take abrasion from wear better than a two ply or a single. On the construction side of it, if you are creating a three ply yarn using the Navajo plying method, you do not need to worry about keeping your bobbins filled equally, or the waste that can be created if one bobbin is more full than the other. Also, as a creative aspect of Navajo plying, you can control the yarn characteristics and create patterns. If you want self striping yarn, the stripes will stay true with the Navajo plying, which would be nearly impossible with any other plying method. Also, you can vary the yarn texture. I like to spin my singles with sections of angora added randomly by holding locks loosely in my drafting hand along with another roving. The effect is more concentrated when the Navajo plying technique is used.
So now that I have you interested in Navajo plying, how do you do it? Spin a bobbin of singles, and either place it on a lazy Kate, or if you only have one bobbin, wind it off and place the ball into a canning jar. Take the leader on the bobbin, and join it to the end of the supply of singles. For this plying method, I find that I have to tie the tow ends rather than just overlapping them. Next, make a large loop as you would to begin a crochet chain, only make it about 12” long. Spin the wheel in the opposite direction to which the singles were spun (usually counterclockwise). As the yarn is twisting, draft the loop back with your normally forward hand, then use your back, or drafting hand guide the yarn from the singles along side the loop until the loop is nearly closed, the with your forward hand, reach through the loop, and grasp the single ply and draw it through the loop. If you think about it, the technique is like making a crochet chain on a very large scale, and adding twist to it. You can still stop periodically to check that the yarn is balanced by letting it go slack between the orifice and your hand to see if it twists in either direction. I do find that the yarn finishes better if you give it a good long soak, and then if it is a wool or camelid yarn to go ahead and full it by agitating it in hot soapy water, then hit it with a cold rinse, and hang to dry.