In knitting, the loops of thread are usually formed by means of a pair of rods called needles. Thread of contrasting colors may be introduced to form patterns. In weft knitting, the regular hand-knitting process that can also be done by machine, the work progresses back and forth; in each course, or new row of stitches, one loop is added to each wale, or chain of loops hanging vertically from the needles. In warp knitting, which is done by machine, the work progresses along the wales. Knitted tubing can be made on spools or circular frames without needles. The yarn or thread is held on a row of pegs that project from and surround the center opening of the spool or frame. Such knitting is also possible when the yarn is held on four of the knitter's fingers instead of on a spool, and it can be made on a large circular needle.
The oldest form of knitting is crossed knitting, in which the stitches, instead of aligning vertically, are rotated a half turn. This method, also called single-needle knitting and pseudo knitting, was highly developed in the fringes of woven cloths produced in pre-Columbian Peru by the Nazca culture (100 BC-AD 700). In the Nazca work, intricate human and animal figures were created by frequent color changes. Other early examples of knitting include pieces from about AD 200, found at the Dura-Europas site near the Euphrates River; sandal socks, apparently from Saudi Arabia from the mid-4th century; and some socks and other items made with the crossed-knitting technique and found in Egyptian burials, the earliest possibly dating from the 4th or 5th century BC. Knitting apparently was introduced into Europe by the Arabs, probably in the 5th century. During the Middle Ages guilds controlled the manufacture of knitted goods such as woolen caps, and the craft flourished in England and Scotland in the 14th and 15th centuries. By 1589 a machine to knit stockings had been perfected in Nottingham by the English clergyman William Lee, whose knitting frame was so excellent that few improvements were needed for 250 years. Later English developments-a ribbing device (1758), a warp-knitting machine (1775), and a circular knitting machine (19th century)-made possible the shaping of hosiery and other garments, and by the 19th century machine-knitted underclothes were common. Commercial knitting centers developed in English cities such as Nottingham and Leicester, and in the U.S. in Germantown, Pennsylvania, and other cities.
As a handcraft, knitting developed both as a folk craft with traditional regional designs and as a popular craft with designs circulating in printed handbooks. In Scandinavia, regional patterns in yarns of contrasting color became characteristic. Other regional styles, such as those of Ireland and the Shetland Islands, were distinguished by different patterns. Another distinctive style to develop was ribbon knitting, in which the use of flat ribbons rather than soft yarns results in a markedly distinctive fabric. In addition to these hand techniques, small knitting machines, which require a high degree of artisanship in their use, also became available to home knitters.