On a knotted pile carpet (formally, a "supplementary weft cut-loop pile" carpet), the structural weft threads alternate with a supplementary weft that rises at right angles to the surface of the weave. This supplementary weft is attached to the warp by one of three knot types (see below), such as shag carpet which was popular in the 1970s, to form the pile or nap of the carpet. Knotting by hand is most prevalent in oriental rugs and carpets. Kashmir carpets are also hand-knotted. Pile carpets, like flat carpets, can be woven on a loom. Both vertical and horizontal looms have been used in the production of European and oriental carpets. The warp threads are set up on the frame of the loom before weaving begins. A number of weavers may work together on the same carpet. A row of knots is completed and cut. The knots are secured with (usually one to four) rows of weft. The warp in woven carpet is usually cotton and the weft is jute.