Wool - Quality Evaluation and Manufacturing Processes

skirting and grading decisions | fleece skirting | table skirting protocol | grading wool | fiber diameter | length of staple | packaging | scouring and cleaning the wool | carding | combing | spinning | weaving and knitting | finishing

Introduction: There are 11 kinds of wool on one fleece (fine and medium wooled breeds), all differing in value to the end user. According to the American Wool Handbook, no two fleeces, even from the same type of sheep and from the same area, are exactly alike in quality and quantity. Unless fleeces are skirted, graded, and sorted, the final wool product will not be as profitable or as consistent. This drawing shows a fine-wooled Rambouillet or Merino. The numbers identify the various parts on the animal that carry the different sorts possible from one type of wool fleece.

The number and name of the corresponding parts for the drawing are as follows:

  1. Top knot: This area has inferior wool that is very light, short, and dirty.
  2. Neck wool: This wool is very light conditioned and long-stapled. It often contains coarse, matted lumps of inferior wool on the folds.
  3. Shoulder wool: The best wool grown by sheep is obtained from the shoulder. Sheep judges usually take the shoulder wool as a standard and see how the wool on the other portions of the sheep compare with it.
  4. Fleece wool: This area contains good, average wool that is usually free from vegetable matter.
  5. Breast wool: This wool is similar to shoulder wool, but is usually a little heavier in condition.
  6. Back wool: This wool is inclined to be open, weathered, and musky.
  7. Britch wool: This is a coarser wool than the other portions of the fleece and is inclined to be kempy. This wool can also be matted and/or cotted with burrs and seeds.
  8. Arm piece: This wool is very short and has very short, open fiber (fribby) edges; burrs or seeds collect heavily on this portion of the fleece.
  9. Hairy shanks: Hairy or kempy fibers containing very little wool are found in these areas; when blended with other wools, they are used to manufacture low quality goods such as rugs.
  10. Stained wool: This wool will not wash white and is very heavy in condition.
  11. Belly wool: This is a bulky wool, heavy in condition, and usually very burry or seedy.

Manufacturing Processes:

  1. Wool Skirting, Grading, Classing, and Sorting: These are post-shearing activities that can enhance the value of any wool clip; however, unless the people performing these operations are trained and skilled, damage and economic losses can occur.
    1. Skirting: Skirting is the practice of separating all inferior fleece portions (head, lower leg, and belly wool) and any urine and fecal contaminated fibers from the rest of the fleece at shearing. The products of skirting are termed skirted wool and skirts. Since large variations exist among skirts from different body areas, these should be packaged separately for technical and economic reasons. Wool from the top of the head, jaw, and cheeks tends to be short and sometimes heavily contaminated with vegetable matter. Belly wool is usually lower yielding and may be either finer or coarser than the bulk of the fleece. It also tends to contain more vegetable and colored fiber contamination than the bulk of the fleece. Lower leg wool is short and tends to be composed predominantly of medullated (coarse) hair fibers. The least valuable of the skirts contain stained fibers and tags. The fibers in this skirt are variable in length, and scouring these fibers results in a relatively low yield of low quality wool. Since the term skirting generally implies removal of all wool that does not match the bulk of the fleece, short wool, matted pieces, paint, skin pieces, areas of the fleece heavily contaminated with vegetable matter, and especially colored wool (stained and pigmented) all fall into the skirts category.

    2. Grading: Wool fleeces differ in many measurable characteristics: fineness, yield, length, strength, color, and vegetable matter contamination. When fleeces are grouped according to any or all of these characteristics, the process is called grading. Wool fleeces may be graded by the grower, warehouse, cooperative facility, scouring facility, or mill.

      The most important measurement of wool quality is "fiber diameter," often called "grade." Average fiber diameter and variation in fiber diameter are directly related to the types of yarn and fabric that can be manufactured. Therefore, fiber diameter is the basic criteria used in establishing the price of raw or grease wool. Finer fibers are usually required in the more expensive fabrics and usually command higher prices. To take advantage of these pricing differences, wool must be graded and placed into more uniform lots. The second most important dimensional measure of wool is "length." Fiber length is a limiting factor which indicates whether wools of a specific grade can be used in the "woolen" or "worsted" manufacturing processes. Worsted is the process that requires "combing." It produces a smoother and stronger yarn when compared to the yarn produced in the woolen system. The machinery involved in combing requires a minimum fiber length for each of the grades. Because worsted yarns are generally more valuable than woolen yarns, fibers that are long enough to be combed are more valuable than short fibers. Fibers too short to be combed are called "clothing" wool. Length also has a direct effect on the yield of a fleece. "Longer" stapled fleeces usually yield more than "short" stapled fleeces.

    3. Classing: The term classing originated in Australia, but is used to mean essentially the same as grading in many areas of the United States.

    4. Sorting: When individual fleeces are subdivided again according to any or all of the above characteristics, the process is called sorting. Sorting requires more skill than grading or skirting. Because of the level of skill that is required, sorting is usually a function performed by a specialized wool dealer or the textile firm itself.

    Skirting and Grading Decisions:
    These decisions are important and should be made in a consistent manner. Practice and experience are essential. The following diagrams and information can be a useful starting point:


    Fleece Skirting: Wool preparation is important in maintaining the quality of the animal fiber clip. This step reflects the attitude of the producer in marketing a useful product to either the industry or individuals. A reputation for a clip is established whether it is on the grading line at a large warehouse, at a processing mill, or being utilized by a home-based business enterprise.

    Fleece skirting, in its simplest method, is sometimes referred to as "floor skirting" and/or "table skirting." Floor skirting is where the belly, head, and leg wool are removed prior to rolling the fleece loose or tying the fleece. Table skirting requires the fleece to be removed from the floor and spread on the skirting table flesh down. A skilled person can remove the fleece from the floor and flip the fleece on the table with the ease of shaking out a blanket. A skirting table is usually 5 feet wide and 8-10 feet in length. Another type of skirting table is one that is circular or round with a diameter of at least 6 feet or more. One popular method of construction is using 1 inch plastic pipe spaced 1 inch apart. This permits the second cuttings, dirt, and vegetable matter to fall through to the floor. An example of this table is shown above.

    Table Skirting Protocol: It is assumed that the belly, head and leg wool was removed on the shearing floor.

    • Remove only wool that does not match the bulk of the fleece. In a well managed flock this means skirting very lightly. Stains must always be taken off. Sweaty edges or sweat locks, short wools, and matted pieces need to be removed from around the edge of the fleece. Do not remove good fleece wool with the skirtings.
    • Skin pieces and clumps of seed or sticks within the wool should be taken out. Stains such as fleece rot and bacterial stain must be removed because they will not scour clean.
    • Rough, kemp laden britches should be removed.
    • All black wool, no matter how small the spot, must be pulled out and kept separate. A few black fibers can ruin an otherwise good lot of wool.
    • Unnecessarily heavy skirting will cost the producer money because good fleece wool is sometimes wasted in the skirted pieces. Neck wool, for example, need only be removed if it contains high vegetable matter or is inferior to the rest of the fleece. If it is similar or better, leave it.

    Fleece Skirting Sections:

    This picture shows the skirting procedure being performed on a round skirting table. A video of this procedure can be found below.


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    Grading Wool
    In the United States wool is graded using one of three methods:

    1. The "American" or "Blood" System: This is an older system where wool is graded depending upon the amount or percent of "fine wool" sheep breeding (Merino/Rambouillet blood) there is in the animal being shorn. For example, if a "grade" ewe is bred by a purebred Merino, the lamb from that mating will produce a 1/2 blood fleece or wool. Currently, the names refer to the diameter of the fiber. With this standard, "fine" refers to the diameter of the fiber, not the total quality of the wool.

    2. The "British," "Bradford," or "Spinning Count" System: This is based on the amount of "Hanks" of yarn that can be spun from 1 pound of scoured (washed) wool. One Hank = 560 yards of yarn. If a Rambouillet grades 64s (fine grade), then 1 pound of clean wool from that sheep will yield over 20 miles of yarn (64 X 560 yards of yarn). This system’s grade numbers are always even numbers, with the lowest being 36s and the highest 120s. With this system the larger number will be a finer wool. The problem with this system is that there are too many variables that influence the results.

    3. The "Micron Count" System: This system was developed in the United States around 1966-67. It is based on actual micron measurements taken with a microprojection unit (magnification 500 X). (One micron = 1/25400th of an inch). Generally, most major wool producing regions of the world utilize this system. It is considered an objective system because it uses scientific measurements to help with the grading.

      Traditionally, the standard method of measuring these fibers is by a microprojection technique in which short longitudinal sections of the fibers are projected onto a screen at 500-fold magnification. Electro-optical and image analysis machines have the capability of measuring 2,000 fibers. An average is calculated, along with a standard deviation and a coefficient of variation. All of this information is gathered, calculated, and printed with a histogram in less than 3 minutes (see figure below). Examples of two of these types of machines are discussed in the following information.
      This is a histogram of wool taken from a Lincoln sheep.

      The Optical Fiber Diameter Analyzer 100 (OFDA100) analyzes 2 mm snippets of the original scoured sample. These fibers are spread automatically onto a glass slide and loaded into the OFDA. The OFDA can measure 4,000 fibers in about 30 seconds. The latest OFDA machine, the OFDA2000, is a portable unit that can analyze grease wool and diameter profile along the staple. The OFDA2000 allows a producer to analyze about 800 samples in 8 hours, while never leaving the shearing pen.

      The Sirolan-Laserscan uses a scoured, 20 g subsample for fiber diameter measurement. The sample is carded using a Shirley Analyzer to remove vegetable matter and blend the fibers in an open web. The web is divided into four sections and placed into a minicore set above the Laserscan. The snippets fall into the Laserscan and are mixed automatically into a solution within the instrument. The Laserscan measures 1,000 fibers from each of the four sections for a total of 4,000 fibers.


    Distribution of Fiber Diameter:
    Individual fibers vary in diameter within any fleece. The britch typically is coarser than the rest of the fleece, even in fine-wool breeds selected for uniformity. In crossbreeds and sheep of coarser wool breeds, it is common to find fibers representing 4-5 spinning counts within the same fleece.

    It is to the manufacturers’ advantage to know how much grade variation exists in any given lot of wool before determining its fair market value. The amount of grade variation is expressed as either the "standard deviation" or "coefficient of variation." Most micron test reports include this information. The standard deviation measures the distribution or variation of fiber diameters around an average. Two-thirds of the fibers’ diameters are within one standard deviation of the average fiber diameter. Highly variable wool will have a larger standard deviation.

    The American Society for Testing Materials (ASTM) has established variability limits for wool fineness. If a wool sample is more variable, or has a higher standard deviation than the one allowed for that grade, the grade is then lowered one spinning count. The "coefficient of variation" is another useful measurement of fiber diameter variability. The coefficient of variation is the fraction or percentage that the standard deviation is of the average. This statistic is most useful in comparing the variation of unrelated groups, such as coarse wool variation versus fine wool variation. A standard of uniformity based on coefficient of variation has been developed for wool and the use of objective measurements. Obtaining side and britch sample micron tests on replacement animals, particularly rams, will be more important as the industry demands higher quality, more uniform wool.

    In general, coarser fibers are stronger and are more resistant to breaking. Although there are no absolute rules, the following products can generally be manufactured from fibers with the associated micron diameters:

    Micron Range Product
    16 -19 Fine worsted and intimate wear
    19 - 23   Apparel, outerwear, quilt-batting, felts
    23 - 28   Sweaters, light upholstery coatings, comforters
    28 - 32 Upholstery, tapestries, some carpets
    32 - 38+ Carpets, industrial use

    British, Bradford and/or Spinning Count System American and/or Blood System Micron System Range for Average Fiber Diameter (Microns) Maximum Standard Deviation
    Finer than 80s Fine under 17.70 3.59
    80s Fine 17.70 - 19.14 4.09
    70s Fine 19.15 - 20.59 4.59
    64s Fine 20.60 - 22.04 5.19
    62s 1/2 Blood 22.05 - 23.49 5.89
    60s 1/2 Blood 23.50 - 24.94 6.49
    58s 3/8 Blood 24.95 - 26.39 7.09
    56s 3/8 Blood 26.40 - 27.84 7.59
    54s 1/4 Blood 27.85 - 29.29 8.19
    50s 1/4 Blood 29.30 - 30.99 8.69
    48s Low 1/4 Blood 31.00 - 32.69 9.09
    46s Low 1/4 Blood 32.70 - 34.39 9.59
    44s Common 34.40 - 36.19 10.09
    40s Common 36.20 - 38.09 10.69
    36s Braid 38.10 - 40.20 11.19
    Coarser than 36s Braid over 40.20 ----
    *According to ASTM Standard Specification D-3991

    Length of Staple:
    Twelve months is considered as the natural growth period for the wool staple. All of its component properties are likely to be developed to the best possible extent in this amount of time. Different breeds of sheep will have very different amounts of wool growth during any 12 month period. For example, the fine Merino breeds may only have a staple length of 1.5 inches in 12 months, while the well fed Navajo-Churros can have a staple length of over 12 inches in that same amount of time.

    Cause of Variations in Length of Staple:
    Variation in length and fiber diameter is due to quite a number of things. The following list contains many of the most common:

    1. Natural or inherited characteristics of the breed: For example, a staple of Lincoln wool should be longer than Rambouillet of the same fineness grown under the same conditions.
    2. Individuality of breed strain or line: Length can be increased within a breed by selective breeding or artificial selection.
    3. Relationship existing between fiber diameter and length: As a general rule, the finer the fiber, the shorter the staple.
    4. Nutrition and health: This is a major factor. An abundance of well-balanced feed stimulates growth, whereas malnourished or diseased sheep grow shorter and finer wool. On a low plane of nutrition, the secondary fibers are frequently more quickly affected in length and fineness, leaving the primary fibers longer and stronger. This produces a wider variation between the two groups.
    5. Age of sheep: As sheep age, the rate of fiber growth slows down.
    6. Climate: Differences in temperature and the animal’s natural environment all have an influence on wool growth rate. For example, the southwestern U.S. and the West are noted for their short fine wools, whereas the Midwest and Pacific Coastal areas produce a longer stapled wool of equal fineness. Studies also show that wool growth rate is increased by an increase in temperature.
    7. Pregnancy and lactation: In the latter stages of pregnancy and when suckling a lamb, a slowing of fiber growth results. This is particularly true when nutrition is low or marginal.

    Length of Staple Affecting the System of Manufacture:
    In most cases, length will decide the purpose for which the wool can be utilized and also the most suitable method of treatment to be adopted. With fine wool, length often determines whether a wool will be acceptable to the worsted or woolen system of processing.

    The worsted processes utilize the longer or "combing" wools. It generally produces a higher grade material. The short stapled wools are more profitably used in the woolen processes. The woolen system produces some high grade materials from short fine wool, as well as absorbing the very lowest types of wool. In the woolen manufacturing processes a high grade "cloth" is manufactured from the short wool (under 2 inches) of good character. Wool of this type is often referred to as "clothing wool." Using the Noble comb or Bradford system, sound wools of 2 inches and over are profitably combed, whereas domestic manufacturers using the Heilmann comb will profitably comb wool 1.5 to 2 inches long. Crossbred wools of around 7 inches and longer in length undergo a preparation process before combing or in lieu of combing, whereas sound wools under that length are carded prior to combing.

    Length in Relation to Strength and Evenness in Yarn:
    In cloth construction, it must be kept in mind that a stronger yarn is made from the longer fibers. For this reason, the longer, sound stapled wools are selected for the manufacture of warp yarn. This yarn has to stand higher tensions and be more elastic during weaving. (Warp is the foundation element of a textile that is strung on the loom and held under tension during the weaving process. Weft is the filler element that is interlaced with the warps to form the fabric.)

    The longer fibered wools that have an even length also give a smoother yarn when spun on the worsted system. This makes the yarn desirable for worsted purposes and particularly warp yarns. For the woolen system, on the other hand, the best and most even yarns are produced with shorter fibers, which are more readily "drafted" in spinning.


    Comparison of Wool Grading Systems with Staple Length Classifications

    American or Blood System British, Bradford or Spinning Count System Combing Staple (inches) French Combing (inches) Clothing (inches) Shrink (%)
    Fine 80s, 70s, 64s 2.5+ 2.5 - 1.0 Under 1 60 - 67
    1/2 62s, 60s 3.0+ 3.0 - 1.5 Under 1.5 52 - 62
    3/8 58s, 56s 3.5+ 3.0 - 2.0 Under 2.0 46 - 54
    1/4 54s, 50s 4.0+ 4.0 - 3.5 Under 2.5 43 - 48
    Low 1/4 48s, 46s 4.5+ ----- Under 4.5 38 - 43
    Common 44s 5.0+ ----- Under 5.0 -----
    Braid 40s, 36s 5.0+ ----- Under 5.0 -----

  2. Packaging: Traditional, original bag (OB) wool packaging procedures require that the belly and perhaps even head and leg wool be placed onto the fleece prior to rolling the whole into a ball. The fiber tips should be to the inside and the shoulder wool on the outside. When packaging fleeces of uniform or single grade, it has become common practice not to tie fleeces. When fleeces of variable grades are being packaged together, the rolled fleeces are normally tied with a paper string. This helps in grading and sorting at the textile mill. Rolled fleeces are then placed into new, clean burlap bags and packed by tramping. These bags may contain 200-300 lbs. of grease wool depending on how the bag is packed (tramping or hydraulic packer).

    Many of the larger producers in the western United States that are selling their individual clips by objective measurement (micron system) and description are packaging their wool in square polyethylene “Ausi-packs.” These are hydraulic packed and can weigh 400-800 lbs.

  3. Scouring and Cleaning the Wool:
    1. Large Scale Commercial Operations: Scouring is the removal of impurities from grease wool. A traditional scouring train consists of four to five rectangular tanks or bowls in which the temperature, waterflow, detergent, and weight of wool passing through the set are carefully controlled. The weight of grease wool scoured per hour in a large commercial unit varies from 3600 lbs. for heavy shrinking, greasy wools to 2400 lbs. for low shrinking or high yielding wools.

    2. Small Scale Operation: A small scale wool washing system generally involves one producer. It could include a small producer cooperative, and/or a producer that custom scours for neighbors. Everything from standard wash tubs to commercial washing machines have been used to wash wool in these small scale operations.

  4. Carding: Carding disentangles and separates scoured wool fibers. Some vegetable matter is also removed during this process. The carding process produces a twistless, rope-like sliver of wool that is prepared for combing or to be used directly in a spinning process. Carding can also be performed by hand, and several types of manually powered carders are available.        
  5. Combing: Combing removes vegetable matter as well as short and tangled fibers from the wool. At the same time, it arranges the long fibers in a more or less parallel configuration, forming a continuous, twistless rope of combed wool. The short fibers combed out are called noils. The combing process is essential to the worsted process. The woolen process, however, does not require combing before spinning. This process can also be done with small human powered tools.      

  6. Spinning: Spinning is the final step in obtaining the desired yarn count or thickness. This process involves the insertion of a predetermined amount and direction of twist and then placement of the yarn into an appropriate package. Spinning is usually accomplished on large, multi-position spinning frames. These frames have multiple speeds to accommodate the spinning of a range of yarn sizes and twist levels. The finished yarns are then evaluated for uniformity, strength, and other important characteristics. There are also many hand spinning units available for weavers and knitters.   
  7. Weaving and Knitting: Weaving is the interlacing of two sets of yarn to form a fabric from which the various types of woolen products can be produced. Knitting is the interlacing of a yarn in a series of connected loops by needles to form a fabric. Yarns are produced for hand knitting and machine knitting. Specialized knitting machines knit socks, gloves, and fully-fashioned flat pieces of material that have no pattern (blanks).

  8. Finishing: From a technical viewpoint, everything that happens to wool fabric after leaving the loom until it is ready for the cutter is regarded as finishing. Much of the wool’s beauty and individuality is developed in these stages. Finishing processes are generally characterized as mechanical, aqueous (including dyeing), and chemical.

Spinners and Weavers: There is renewed interest in the U.S. in quality, handcrafted woolen products.  Spinners and weavers constitute a specialty or niche market for certain types of wool, usually bringing premium prices.  The development of fleece shows and sales can be used to encourage spinners to be present where fleeces are auctioned off. The type of wool desired by this market include the following: 

Summary: Although wool and mohair are the least understood of the American small ruminant industries, it is hoped that the information presented will enhance the knowledge of the readers and producer. Today, marketing of lambs and kids is a challenge due to market concentration, but even more problems exist when marketing the fibers produced by the small ruminants. Although international markets continue to have a negative impact on the U.S. wool and mohair producers, niche marketing and value-added activities are helping to improve the U.S. domestic markets. Producers today are having to expand their understanding of fiber production and the positive attributes of their animal fibers.

More and more, consumers of wool and mohair products realize that these natural fibers have unique characteristics that synthetic fibers cannot match. The end consumer is also demanding better products. This results in more emphasis being placed on grading and quality evaluation of these raw fibers at the producer level. Thus, fiber grade or diameter, and fiber class or staple length must remain part of the producer’s year-round production goals.

Finally, it is important to consider that the wool and/or mohair product can result in as much as 20 percent of the gross annual revenue for a producer. In order to take advantage of this potential revenue, producers must be aware of breed differences in fleece and fiber production. The producer must also be aware of environmental influences that can damage the fleece or fiber and hinder its growth.

Sheep Breeds and Their Wool Characteristics:

Sheep Breeds Diameter
Grease Fleece Weight
Clean Fleece Yield
Border Leicester 38 - 30 8 - 12 60 - 70
Cheviot 33 - 27 5 - 8 50 - 65
Columbia 30 - 23 9 - 14 45 - 55
Corriedale 31 - 24 9 - 14 45 - 55
Debouillet 23 - 18 9 - 14 45 - 55
Delaine-Merino 22 - 17 9 - 14 40 - 50
Dorset 33 - 27 5 - 8 50 - 65
Finnsheep 31 - 24 4 - 8 50 - 70
Hampshire 33 - 25 5 - 8 50 - 60
Lincoln 41 - 34 10 - 14 55 - 70
Montadale 30 - 25 5 - 9 45 - 60
Oxford 34 - 30 5 - 8 50 - 60
Rambouillet 23 - 19 9 - 14 45 - 55
Romney 39 - 32 8 - 12 55 - 70
Shropshire 33 - 25 5 - 8 50 - 60
Southdown 29 - 24 5 - 8 40 - 55
Suffolk 33 - 26 4 - 8 50 - 60
Targhee 25 - 21 9 - 14 45 - 55