I just wound a linen warp of 35/2 linen and the threads were quite twisted as I sleyed, threaded, and beamed the warp. What was I doing wrong?
Most linen is packaged on spools that are 5–6" long and relatively narrow (2" or narrower in diameter when they are full). If you place this spool on an upright rod (the way you might place a cone) and pull the yarn off the end of the spool, you either add twist to the yarn in one direction or the other, depending on which end of the spool is up. With the narrow spools typical of linen packaging, this would be the same as adding a full twist to the yarn for every 5 or 6" of yarn length. (Most 2-ply yarns are made of two single Z-twist yarns plied together with an S twist. The label "Z" or "S" identifies the way the diagonal twist direction looks when you hold the yarn vertically. A plied yarn is usually relatively inert; therefore twist is added to the yarn no matter which way the yarn unwinds.)
The best way to unwind yarn from a spool is to place it on a horizontal rod so that the spool can turn as the yarn unwinds, thereby not affecting the yarn twist at all. Spool racks make this easy. If you don't have a spool rack, you can place a metal rod (cut a piece from a wire clothes hanger if nothing else is available) thorough the slats of a plastic crate (of the milk crate ilk). If you place the spool in a container, such as a box or bowl, it will mostly unwind the way it would on a rod, but occasionally the yarn will pull off the end.
You might wonder why this same issue doesn't occur with cones of yarn, since the yarn is almost always pulled off of the ends of a cone that is placed upright. The answer is that it does. Usually, though, coned yarns are more flexible than linen (most linen comes on spools) and do not present as much difficulty if they are twisted. The circumference of a cone is also larger, therefore less twist is added. There are, however, cone holders available that will allow a cone to rotate so that the yarn unwinds from it the same way it does from a spool on a horizontal rod. And, you could achieve the same result by placing the cone on a horizontal rod in a plastic crate.