Heddles are devices that control the warp, or lengthwise, threads during the weaving process. In weaving on the simplest looms, a person manually maneuvers the weft, or crosswise, thread over and under the warp threads. On more complex looms, heddles control the warp threads. The entire assembly of heddles and their framework is the heddle shaft, or harness. When a weaver lifts the harness, the warp yarns — controlled by the heddles — lift, thereby creating a shed, or open space, for the shuttle with the weft yarn to pass through.
To use heddles, a person raises the harness, which then pulls up the heddle-tied warp, to create the first shed — a tent-like opening between the warp threads. This is the upper shed. The weaving shuttle, which holds the weft, is then passed through the open shed. Next, the harness is pulled down to create the lower shed and the shuttle is passed through it. On looms that have multiple harnesses, weavers read a draft or pattern to determine when to lift each harness.
Of the two types of heddles — suspended and rigid — the easiest to learn generally is the rigid heddle. This is simply a piece of wood or plastic with alternate slots and holes that the warp is threaded through. When the heddle is raised, the warp in the holes is lifted and the warp in the slots is not. The suspended heddle assembly is usually made of string or wire heddles in a harness. Sometimes, the ones made of string can become tangled or break, thereby making them more difficult for beginners.
Heddles are made of various materials. Which type of material a weaver uses for a heddle is mostly personal preference. Some weavers believe string is gentler to the warp yarns; others find flat steel is stronger and less likely to break. Rigid heddles can be made of cardboard, wood, or plastic. Suspended ones typically are made of string, wire, Texsolv, or flat steel.
Some manufacturers offer different styles of wire heddles, such as regular, long eye, and inserted eye. Wire or flat steel strip ones sometimes tend to chafe or break the warp; various wire styles have solder around the hole where the warp goes through to minimize this damage. Texsolv heddles are made of crocheted, heat-treated polyester and are strong and lightweight, which makes the harness lighter to lift. Rigid heddle looms use wooden, plastic, or even cardboard assemblies.
Specialty heddles address the problems that unique weaves pose. For example, in leno weaving, the warp and weft yarns cross each other. Leno, or doup, heddles combined with special frames allow the weaver to efficiently create attractive fabric. Others include twin wire, narrow fabric, or repair heddles, which replace broken heddles.