Preparing wool begins with picking, or separating, the fibers by hand to remove dirt and foreign material, followed by washing, another round of picking, and carding. Carding uses two wire-toothed brushes to straighten the fibers and remove tangles, producing a loose roll called a rolag. The spinner then draws the wool from the rolag while turning the spinning wheel, adding twist to form yarn that is wound onto the spindle. Spinners often alternate between picking, carding, and spinning to vary the work and rest. The finished yarn is usually plied by twisting two or more strands together for strength, then wound into skeins, washed, and sometimes dyed before being used for weaving or knitting.