Woven cloth is normally much longer in one direction than the other. The lengthwise threads are called the warp, and the other threads, which are combined with the warp and lie widthwise, are called the weft (synonyms are “filling,” “woof,” and “shoot,” or “shute”). An individual thread from the warp, of indefinite length, is called an end; each individual length of weft, extending from one edge of the cloth to the other, is called a pick, or shot. Consecutive picks are usually consecutive lengths of one piece of weft yarn that is repeatedly folded back on itself.

In all methods of weaving cloth (except the rudimentary form of darning), before a length of weft is inserted in the warp, the warp is separated, over a short length extending from the cloth already formed, into two sheets. The process is called shedding and the space between the sheets the shed. A pick of weft is then laid between the two sheets of warp, in the operation known as picking. A new shed is then formed in accordance with the desired weave structure, with some or all of the ends in each sheet moving over to the position previously occupied by the other sheet. In this way the weft is clasped between two layers of warp.

Since it is not possible to lay the weft close to the junction of the warp and the cloth already woven, a further operation called beating in, or beating up, is necessary to push the pick to the desired distance away from the last one inserted previously. Although beating in usually takes place while the shed is changing, it is normally completed before the new shed is fully formed.

The sequence of primary operations in one weaving cycle is thus shedding, picking, and beating in. At the end of the cycle the geometrical relation of the pick to the warp is the same as it would have been if the pick had been threaded through the spaces between alternate ends, first from one side of the cloth and then from the other, as in darning. This is the reason the weaving process is considered an interlacing method.

Early development of the loom

The word loom (from Middle English lome, “tool”) is applied to any set of devices permitting a warp to be tensioned and a shed to be formed. Looms exist in great variety, from the bundles of cords and rods of primitive peoples to enormous machines of steel and cast iron.

Except on certain experimental looms, the warp shed is formed with the aid of heddles (or healds). Usually one heddle is provided for each end, or multiple end, of warp thread, but on some primitive looms simple cloths are produced with heddles provided only for each alternate end. A heddle consists of a short length of cord, wire, or flat steel strip, supported (in its operative position) roughly perpendicular to the unseparated sheet of warp threads and provided, in modern looms, with an eyelet at its midpoint, through which the warp end is threaded. By pulling one end of the heddle or the other, the warp end can be deflected to one side or the other of the main sheet of ends. The frame holding the heddles is called a harness.

In most looms, the weft is supplied from a shuttle, a hollow projectile inside which a weft package is mounted in such a way that the weft can be freely unwound through an eyelet leading from the inside to the outside. The shuttle enters the shed and traverses the warp, leaving a trail of weft behind.

Beating in is generally effected by means of a grating of uniformly spaced fine parallel wires, originally made of natural reeds and thus called a reed, which, mounted at right angles to the warp, oscillates between the heddles and the junction of the warp and the cloth. The ends pass, one or more at a time, through the spaces between consecutive reed wires, so that the reed, in addition to beating in, controls the spacing of the ends in the cloth.