Wool, common name applied to the soft, curly fibers obtained chiefly from the fleece of domesticated sheep, and used extensively in textile manufacturing. Wool may be differentiated from hair mainly by the nature of the scales that cover the outer surface of each fiber.
Wool scales are numerous, minute, and pointed and are attached only at their bases; thus the fibers interlock under pressure (see Felt). The number of scales varies with the fineness and curliness of the fiber. Because of its crimp, or curl, wool has considerable resilience. This quality, together with its high tensile strength and elasticity, gives fine woolen fabrics the ability to retain shape better than cloth made from other natural fibers. Other characteristics of wool, which make it especially desirable for clothing, are its lightness, its ability to absorb moisture, and its insulating properties.
Wool production begins with several basic concepts. Along with the fiber diameter, the fiber length, and the amount of vegetable matter and any other foreign material in the fleece affect wool quality. Fiber diameter varies by breeds of sheep and is used to determine the use of the wool. Wool made up of smaller diameter fibers or fine wool is used for clothing while wool made up of larger diameter fibers or coarse wool is used for carpets and rugs. Below are more details about wool production and wool quality.
As wool comes off the sheep it is called grease wool. This is because the lanolin in the wool gives it a greasy feel and appearance. This wool also contains vegetable matter, dirt, and other impurities. Wool goes through a scouring process to remove the grease, dirt and other impurities, and a carbonization process to remove vegetable matter. The difference between the grease wool weight and the clean weight is the yield. In general, fine wool fleeces have a lower yield than medium and coarse wool fleeces. Much of this also depends on the amount of grease in the fleece. Expected yields range from 45% to 70%.
Fiber diameter is probably the most important factor for determining the quality of wool and its value. As the fiber diameter increases, it changes the way wool is used. Larger diameter fibers do not work well in the felting process, but because they are stronger and less likely to break during the carding and combing process, they are very well suited for carpets and rugs. Small diameter fibers or fine wool are best suited for clothing and textiles.
Fiber diameter is used to determine the wool grade. The American system began by visually appraising the wool fibers. This system is known by the blood grade because it starts with the Merino breed and the wool from other breeds is graded according to the percentage of Merino in the breed. Table 1 shows the various wool grades using both the American Blood Grade system and the ASTM (American Society for Testing and Materials) standard grade. The number corresponding to the ASTM grade related to the number of 560 yard lengths of yarn that can be spun from one pound of a top (clean wool).
Crimp is another wool characteristic highly related to fiber diameter. Crimp is the waviness of the wool. High-crimp wools that are very uniform are normally the higher quality wools. However, wool with too much crimp can cause problems in the processing the same as wools with very little crimp. Low-crimp wools tend to tangle and felt during scouring while high crimp wools can form balls or “neps” during carding and combing.
Vegetable matter in wool comes from feed particles as well as burs, seeds, twigs, leaves, and grasses. Vegetable matter is removed from a fleece using a process called scouring. A certain amount of vegetable matter is expected in wool, however, an excessive amount is considered a defect and the wool may be discounted in price.
Several ways to minimize the amount of vegetable matter in wool include the following: removing belly wool, wool on the top of the head and around the cheeks, and removing manure clumps or tags. Carefully feeding sheep to prevent contamination can also decrease the amount of vegetable matter in the wool.
Fiber Length and Strength
The staple or fiber length affects how the wool can be used. Very short fibers are used in the felting process. There are three classes of staple length: staple, French combing, and clothing. The length of the wool fiber has a direct effect on spinning speed, yarn count, and yarn quality.
The whiteness of wool is very important if the fibers are not expected to be dyed or will be dyed a light color. White wool fleeces come from fleeces that have been skirted to remove any urine or feces-stained wool. Producers who wish to market a very high-quality wool keep their sheep covered year-round to prevent contamination and discoloration of the wool. The presence of colored fibers in wool has an effect on the price of that wool also due to limiting the uses of the wool. These fibers can come from the sheep themselves, either dark fibers in the wool or from head, belly or legs. They may also come from stained wools. Colored wools from natural colored sheep are generally a specialized market for people who spin or weave by hand. Sold to a mainstream market, these wools are discounted because of their limited use in the dying process.
Cotted or Felted Fleeces
Occasionally, the wool fibers may become matted or felted together. This occurs when fine fibers have a very little crimp. Cotted or felted fleeces are considered low quality because of the amount of waste produced during carding due to breaking the fibers when they are torn apart. Fine wool sheep that have very little crimp should be culled.
The Merino is an economically influential breed of sheep prized for its wool. Merinos are regarded as having some of the finest and softest wool of any sheep.
Following are the common breeds of Merino Sheep:
- Booroola Merino
- Delaine Merino
- Fonthill Merino
- German Mutton Merino
- Medium-Wool Merino
- Poll Merino
- South African Merino
- South African Mutton Merino
- Strong Wool Merino
The sheep was one of the first animals to be domesticated over 8000 years ago. Sheep were usually seen with humans on the move because they could be herded easily and they provided humans with their basic needs – food, clothing, and shelter. For the early Stone Age hunter, the fleece served as a tunic or sleeveless shirt, worn just as it came from the animal’s back. The first weavers used reeds, threads or grass to make baskets and nets. By Neolithic times, a simple loom had been invented and the art of weaving was well on its way.
As early as 4000 B.C. wool clothing was worn in Babylon, Babylon means “Land of Wool”. Fifteen hundred years later, nations of the East began to trade wool, thus making it one of the early items of international trade.
From Fiber to Fabric
Once each year the sheep can give us the coats off their backs. The wool is removed with shears similar to those a barber uses. This process of shearing does not hurt the sheep. In about five minutes the wool is shorn from the sheep in a single piece, called the fleece. The fleece is carefully rolled and tied for bagging. Most shearing is done between February and June, just before lambing. Most shearers move from ranch to ranch. A good shearer can shear from 80 to 125 head of sheep a day. A highly trained expert can shear up to 225 head of sheep in one day.
Fleeces are rolled up and tied, then packed into sacks. These sacks hold between 20 and 35 fleeces (of 4-12 lbs each) and weigh an average of 200 to 400 pounds. From this step, the processing of the wool begins.
The wool is washed by moving it gently with rakes through a series of tubs containing a soap and water solution heated to about 140°F. It is then rinsed. During the washing, process wool loses 30 to 70 percent of its weight when natural grease (lanolin) and soil are removed. After washing, the wool is passed through a series of squeeze rollers and finally dried. The purified lanolin by-product is used in face creams, soaps, and other ointments.
Wool can be dyed at several stages in the processing – after it has been washed, in which case it is called stock-dyed wool; after spinning, when it is referred to as yarn-dyed wool; or after weaving or knitting when it is called piece-dyed. Because wool is a porous fiber, color tints are absorbed right into its core to give rich and lasting hues.
Carding blends wool fibers remove vegetable matter and straighten the fibers so they will lie in the same direction. This is done by passing the wool through a system of rollers covered with wire teeth which form the fibers into a thin web. If the wool fibers are to be made into fabric, the web is divided into strips which are rubbed together gently to form the “roving” or “sliver.”
Spinning draws strips of roving through small rollers, applying a twist that gives the resulting yarn strength and size. The difference in size, twist, and ply give the woven fabric different texture which is part of fabric design.
Woven fabrics are made on looms by interlacing at least two sets of yarn at right angles to each other (put another way, weaving involves two pieces of yarn running in different directions, one up and down, and one across). The lengthwise (or up and down) yarn is the warp. Yarn running crosswise in the loom is called weft or filling. As warp yarn passes through the loom it is raised and lowered by a wire eyelet through which it is threaded. To form the woven fabric, filling yarn is pushed through openings created in the warp.
As the fabric comes from the loom it has a loose texture. Fulling or milling by the application of moisture, heat, and friction causes the material to shrink and thus tighten the weave. The fabric can then be napped by a metal brushing process, or sheared to give a smooth, uniform appearance. Various chemical finishes can be applied to obtain such advantages as mothproofing, stain resistance and washability.
Processes in the Wool Industry
BY-PRODUCT – something produced in addition to the main product. In the case of sheep, wool and meat are the major products. Other products that come from the sheep are lanolin for cosmetics; hides and skins for leather goods; gelatin for photographic film; animal fat for soap and special glues and medicines – to name only a few.
CARDING – blending and straightening out the wool fibers.
DYEING – to impart color to something.
FLEECE – coat or wool covering a sheep.
FULLING – applying moisture, heat, and friction to wool fabric to cause the weave to tighten.
Wool is the natural fiber sheared from sheep. Wool is a renewable resource because it grows back every year. Different breeds of sheep grow different kinds of wool. Most wool is white but some sheep have wool that is black, grey or brown. These sheep are called natural colored sheep. There are many different kinds of natural colored sheep.
Sheep can grow fine wool, medium wool, or coarse wool. Fine wool is often used to make suits and clothes. Medium wool is often used to make blankets. Coarse wool is often used to make carpets. Wool from natural colored sheep is usually used to make specialty items and yarns because of its color. Many items like knitted sweaters, caps, gloves and scarves are also made from wool.
Over 8,000 years ago people domesticated sheep. Sheep were one of the first animals to be herded by humans. Sheep helped provide people with food, clothing, and shelter. As humans moved from place to place, sheep were easy to herd and take with them.
Buying and selling wool cloth was important to many areas. As early as 4,000 B.C. woolen cloth was being used in the city of Babylon. Babylon means “land of wool.” Today, there are over 1 billion sheep in the world and more than 200 different breeds.
There are over 35 kinds of breeds of sheep in the United States. There are over 200 different breeds of sheep in the world! All these different breeds of sheep can be divided into two main groups – meat breeds and wool breeds. Most of the time the meat breeds have black faces and the wool breeds have white faces. Meat breeds are primarily raised for food and wool breeds are primarily raised to produce fiber. Both produce food and fiber.
Most lambs are born in the spring. Mother ewes can give birth to one, two or three lambs. Some ewes have had as many as five lambs at once! Lambs weigh between seven and fifteen pounds when they are born. Lambs can stand soon after they are born. The mother ewe cleans them off. Lambs drink their mother’s milk and grow strong. Soon, lambs will eat grasses and hay like their mother. Lambs stay with their mother until they are five months old.
Sheep grow fluffy wool over most of their bodies. Wool keeps them warm and dry. Sheep must have a haircut once a year. This is called shearing. Sheep grow a new coat of wool every year. Shearing does not hurt the sheep. Shearing is most often done in the spring. This way a sheep does not have to wear a wool coat all summer! The wool from one sheep is called a fleece.
Sheep are sheared in the spring. Their wool or fleeces are put in large sacks and sent to a woolen mill for processing. The fleeces are washed to remove dirt, grass, and lanolin. After the wool is clean and dried it is combed or carded. Carding makes the fibers straight. The next step is spinning the wool into yarn. There are two types of yarn – woolen and worsted. Woolen yarn is used to make carpets or thick sweaters. The worsted yarn is knitted or woven into cloth that is used to make shirts, dresses, suits and other woolen garments.