met again when a new batch is dyed, the colour of the pile changes when a new row of knots is woven in. As such, the colour variation suggests a village or tribal woven rug, and is appreciated as a sign of quality and authenticity. Abrash can also be introduced on purpose into a newly planned carpet design. Techniques and structures The process of weaving a rug The weaving of pile rugs is a time-consuming process which, depending on the quality and size of the rug, may take anywhere from a few months to several years to complete. To begin making a rug, one needs a foundation consisting of warps and wefts: Warps are strong, thick threads of cotton, wool or silk which run through the length of the rug. Similar threads which pass under and over the warps from one side to the other are called wefts. The warps on either side of the rug are normally plied into one or more strings of varying thickness that are overcast to form the selvedge. Weaving normally begins from the bottom of the loom, by passing a number of wefts through the warps to form a base to start from. Knots of dyed wool, cotton or silk threads are then tied in rows around consecutive sets of adjacent warps. As more rows are tied to the foundation, these knots become the pile of the rug. Between each row of knots, one or more shots of weft are passed to keep the knots fixed. The wefts are then beaten down by a comb-like instrument, the comb beater, to further compact and secure the newly woven row. Depending on the fineness of the weave, the quality of the materials and the expertise of the weavers, the knot count of a handmade rug can vary anywhere from 16 to 800 knots per square inch. When the rug is completed, the warp ends form the fringes that may be weft-faced, braided, tasseled, or secured in other ways. Looms Looms do not vary greatly in essential details, but they do vary in size and sophistication. The main technical requirement of the loom is to provide the correct tension and the means of dividing the warps into alternate sets of leaves. A shedding device allows the weaver to pass wefts through crossed and uncrossed warps, instead of laboriously threading the weft in and out of the warps.