Sheep Wool is a kind of protein string which grows on sheep fur, an important material in carpet weaving. In every string of wool, there are three main parts, from outer part to inner section standing as follows:
1- Outer cover
2- Inner layer
3- Marrow of the wool
Tension rate of wool cord is about 1/3 of the actual length, much more than cotton; so it is used scarcely for warp and weft, because cords have spring quality and can not stay stable enough on the loom. Carpets with woolen cords become sinuous in the course of time - like tribal carpets.
In Iranian vast plateau, not withstanding to dry climate, there are flourishing prairies for raising live stocks in the slopes of Alborz and Zagros, specially around Sanandaj, Kermanshah Northern Khorasan, Baluchistan and central regions; There raise sheep, which their excellent wool would be used in weaving durable foot-resistant carpets.
Most Iranian sheep are from "Hetrotype" race; cord of their wool is coarse, thick and strong enough for carpet weaving. Thickness of the wool of Iranian sheep, size between 35 to 50 microns and its length, sometimes stretches to 35 cm. Sheep, living in mountains have a better wool due to humidity and become much better if it is cut in spring time. Sheep with pure white wool, mostly of Systan, breed their wool become much fragrant after dyeing.
Wool when cut from the sheep fur, has a lot of alien materials, which must be filtrated before spinning. Those aliens are: Fat (Lanolin), Urine and sweat of animal dried on the wool surface, having potassium, mineral and organic Acids. To separate those materials, wool filaments must be washed, then the remaining water must be dropped out and be dried on a clean bed uniformly. These operations are done by hand or in wool-washing workshops, equipped with mechanical washers and driers.
Explaining specifications of wool, it must be beckon that the more filaments of wool are thinner and longer, the quality is much better. Strength of wool has a direct relation with feeding of animal. The better nutrition, makes the better and stronger wool. Wool is in different colors. Pure white wool is the best and the most expensive, because it might be dyed at any desired color, without chemical operations, that results less strength of filaments. Pure white wool becomes yellowish and weak by carelessness. Dye ability of wool depends on:
1- The primal color of the wool
2- Level of fat to be washed out or minimized
3- Thickness of filaments, the thinner, the better for dye ability and permanence
Therefore, a first class wool is the washed up wool, with white color, and the contamination of its filaments not more than 25%, the medium thickness of its filament at 30 microns and medium length of its filaments, not less than 7.5 cm.