On my Lendrum wheel I spun a medium twist single. With the grey yarn shown in following photos, I tried for a loose twist. As of today I have spun three bobbins full of a slick mohair single (this gold-pink-brown; a natural grey shown below; and a gold-orange-green).
The boucle burn happens in the second step, which is the first plying step (ply S twist). A thin but strong core thread is plied along with this mohair single. I am finding that after a short time the friction of the core thread running over my right index finger starts to make it sensitive. So I have taken to applying some painter's tape to that part of my finger to prevent the "boucle burn". As the mohair is applied to the core you push up the loops periodically to store them in clumps on the core thread.
I will try to get some more photos of the intermediate steps. The second plying step is to take a binder thread ( and I have been using an even finer thread for this stage; thus more threat of my finger catching fire....) and ply it to the two ply, with a Z twist. In the two yarns that are complete, the binder I used was simple polyester sewing thread. The clumps of loops have to be opened up and spread out as you ply. Yes, it is an art form! I did all the plying on my Louet S-10 since I had lots of bobbins available for that wheel.
In this close up you can see a pale core thread ( very pastel pink-blue-beige), with the grey mohair loops arrayed around the core. Then the thin black thread is applied as the binder to keep the loops where you want them.
Here is the finished skein of the natural grey mohair. I just love how the light dances over the little circles. This yarn is so very soft. It will be tricky to knit with, not allowing for any "ripping back".
And here it is in a twisted hank. It is ready for knitting or weaving with. I also have a hank done of the the gold-orange and green, but need a "sunshiny" moment to photograph it. And the gold-pink-brown that we started this post with will be plied and made into a boucle next week, at our next spinning guild meeting.