Shed (weaving)

In weaving, the shed is the temporary separation between upper and lower warp yarns through which the weft is woven. The shed is created to make it easy to interlace the weft into the warp and thus create woven fabric. Most types of looms have some sort of device which separates some of the warp threads from the others. This separation is called the shed, and allows for a shuttle carrying the weft thread to move through the shed perpendicular to the warp threads. Which threads are raised and which are lowered are changed after each pass of the shuttle.

The process of weaving can be simplified to a series of four steps: the shed is raised, the shuttle is passed through, the shed is closed, and the weft thread is beaten into place. These steps are then repeated, with a different set of threads being raised so as to interlace the warp and weft.

The term shedding refers to the action of creating a shed. A shedding device is the device used to raise or open the shed. Creating the separation is referred to as raising or opening the shed, while the reverse is known as lowering or closing the shed.

The type of device that is used to raise and lower the shed differs on the type of loom. With a tablet loom the sheds are raised and lowered by rotating the tablets, or cards. In a floor loom the shed is created by the harnesses. Inkle looms have one of the more primitive shedding devices, where there is one set of heddles and the shed is created by hand.

Originally there was no shed, and the weft was inserted into the warp by picking the warp threads up individually, as is done in tapestry weaving. After each weft thread is woven the warp threads had to be picked out and lifted again, which made the process slow. To speed up the process various devices were developed to create a reproducible shed, so that the weft could be passed between the separated threads, and so the threads would not have to be separated individually each time. The first type of shedding device was called a shed-rod. It was a rod inserted into the warp to ease in weaving, and came about at the same time as the heddle. Threads were alternated over and under the rod, and the threads that went under the rod went through string heddles attached to a bar. The shed was created in two ways:by raising the shed-rod, and by lifting the heddles. The shed-rod was an invention of eastern origin, and was introduced to Europe via Egypt in the first century AD. The Romans used it for both plain weave and twill.

...
Wikipedia