In the early Middle Ages, most weaving was done at home for the family’s own use. By the late period, most weaving was commercial, carried out as a full-time craft by professionals. The key shift was in equipment cost, and this took place when the horizontal loom’s greater efficiency made it a mandatory investment.
The loom used all across Europe, until the 12th century, was the vertical frame loom. It could weave a piece of cloth as large as the frame, and no larger. In Scandinavia, where vertical looms were still used long after they’d been abandoned in the south, the warp threads hung down straight from the top beam, held tight in clusters by metal doughnut weights. The weaver began at the top and worked downward. Outside Scandinavia, the warp threads were tied to the bottom of the frame and looped over the top beam—and then hung down, held tight in clusters by metal doughnut weights. These looms were worked by starting at the bottom and moving up.
I have to admit here that I’m not super clear on how the vertical loom was managed, but this is the best I was able to figure out: the warp threads looped around a beam so that the threads did not lie flat with each other, but were at first separated by the width of the beam. It was easy enough to pass a shuttle between them. The trick was to reverse the order, so that the behind-lying one came forward. This was accomplished with a long heddle stick; it had short strings tied to these back-lying warp threads. When the weaver pulled it forward, the warp threads crossed and now the weft shuttle’s pass locked the previous weft in place. Without forward tension on the heddle stick, those threads again hung back. Every other shuttle pass required the heddle stick to be pulled forward. Another method just used two heddle sticks, with each one attached to a different set of alternating warp threads.
There were some real drawbacks to this loom. It required three hands: one to pull on the heddle stick, and two to pass the shuttle through. It made the weaver stand up all day, and eventually the weaver was bending in an uncomfortable position and then squatting. Chiefly, never mind these discomforts, it could only make a piece of cloth as big as the frame. Some late improvements allowed the top or bottom beam to wind up finished cloth and expose more warp, but most of the time, this wasn’t so. Ship sails were pieced together out of squares. Ever notice that cartoon viking ships had striped sails? Each stripe would be as wide as the frame loom.
The horizontal counter-balance loom is familiar to us because its technology has changed little since the 12th century. Back and front beams wind up the warp, slowly rolling up finished cloth at the back and unrolling more thread at the front. In the center, a vertical “castle” has free-moving racks that can lift (via foot pedals) every other thread or any other pattern you want. Once these looms had two heddle frames, it wasn’t long until weavers noticed that four or six made the loom no harder to manufacture or operate but allowed for twills, diaper weaves, and even weaving a tube. Not only that, but the looms could be made double-wide with a bench for two men to sit, each one throwing or catching the shuttle that now moved slickly along a floor of warp threads.
The problem was that these looms were very expensive. Home weavers couldn’t build them out of a few sanded tree trunks, and they needed special metal parts beyond lead doughnuts. So weaving became a professional craft. Weaving workshops tended to be staffed by men who did not own the equipment, so they were the first step toward factories with hourly laborers, in an economy otherwise filled with tool-owning self-employed craftsmen.