This section is from the book "Clothing For Women: Selection, Design, Construction", by Laura I. Baldt. Also available from Amazon: Clothing For Women: Selection, Design, Construction.
Every time the woof goes back and forth, it passes around the outer warp thread, thus forming the Selvedge on each side of the cloth.
For fancy weaving more heddles and sometimes more treadles are necessary, so that different arrangements of warp threads may be raised or lowered in order to produce a more or less fancy effect. This is done by tying certain combinations of heddles and treadles together, when one or more treadles are pressed down, certain heddles will be raised, others lowered, and all warp threads passing through each of the heddles must work together each time.
Hand Looms are usually built of wood and are worked by foot power on the treadles, the shuttle is thrown back and forth by hand, and the battening up of the filling is done by hand.
The framework, etc., of this loom are usually made of cast iron, some few parts may be of wood. The motive power is water or steam, or, in modern looms, direct connected electric motors, and the harness is operated from below.
The above, known as " Harness Looms," are necessarily limited as to the number of patterns which can be carried out on them. But there is a machine called the "Jacquard Loom" upon which an almost unlimited variety of pattern may be carried out, e.g., brocaded silks, ribbons, and linen (damask). Jacquard Loom is not a correct expression, however, as the loom or weaving method of putting in the filling and battening up is the same as in all looms, but the shedding mechanism is different. Instead of a harness composed of heddles, each of which controls the same threads each time, and is operated from below, the Jacquard attachment is above the loom, each heald hangs independent of all others, and can be operated independently, or in combinations with any others called for by the design being carried out. Each heald is attached to a vertical wire which has a hook on its upper end by which it hangs on a bar, but can be easily displaced or thrown off. Each wire passes up through an eye in one of a group of horizontal needles. At one end these needles, which work horizontally, enter a spring box which keeps them constantly pressed forward. At the opposite ends the needles pass through and project beyond the "needle board," where they come in contact with a four-sided cylinder placed at right angles to the ends of the needles - each one-quarter revolution of the cylinder brings one of its side in contact with the needle ends. Over this cylinder pass cards with holes cut in them at each place where a needle end comes in contact with it. If holes are cut for all needles, they will all pass through and all the vertical wire hooks will be held in position to be lifted by the bar on which they are hung. Thus all warp threads will be lifted and no shed made, but if the places on the card for some needles remain blank or uncut, it will readily be seen that those needles will be held back, their vertical wire hooks thrown off the bar and so not lifted. Therefore, all these warp threads will remain down and a shed be made. So, for every shed of one repeat of a pattern, there will have to be a different card; these are laced together so that they pass in regular order over the cylinder.