Wool is primarily graded by classifying the whole fleece according to its fineness (fiber diameter) and length. This classification is crucial for determining the wool's quality, its suitability for various textile products, and ultimately its market value. Expert graders meticulously examine the wool, also paying close attention to the fiber's natural waviness, known as crimp, which is a strong indicator of its fineness.
Key Factors in Wool Grading
Several characteristics contribute to a wool's overall grade, with fineness and length being paramount.
Fineness (Fiber Diameter)
Fineness is the most critical factor, referring to the individual wool fiber's diameter. It is objectively measured in microns (µm), where one micron equals one-millionth of a meter. Finer wools have smaller micron counts, resulting in a softer feel, better drape, and higher value, making them ideal for next-to-skin apparel. Coarser wools, with larger micron counts, are more durable and suited for outerwear, carpets, and industrial uses.
Length
The length of the wool fibers, often referred to as staple length, is vital for processing. Longer fibers are generally preferred because they can be spun into stronger, more uniform yarns with fewer breaks. Wool is typically categorized into different staple lengths (e.g., combing, French combing, clothing) based on its suitability for various spinning processes.
Crimp
Crimp is the natural waviness or undulation of the wool fiber. A grader observes crimp because the crimp count per inch (2.5 centimeters) usually correlates with fineness:
- Finer grades tend to have a higher crimp count (more waves per inch).
- Coarser grades typically have a lower crimp count (fewer waves per inch).
Crimp contributes to wool's elasticity, resilience, and insulating properties by trapping air.
Other Important Characteristics
While fineness, length, and crimp are primary, other factors also influence a fleece's grade:
- Strength/Soundness: Refers to the fiber's tensile strength and whether it has weak spots or breaks, often caused by poor nutrition or stress in the sheep. Strong, sound fibers are essential for durable textiles.
- Color: Most wool is white or off-white, which is preferred for dyeing. Discolored wool (e.g., yellowing from urine or stains) reduces its value.
- Purity: The absence of undesirable fibers like kemp (hollow, brittle fibers) and medullated fibers (fibers with a central air-filled canal) is crucial. Also, the presence of vegetable matter (burrs, seeds, straw) or foreign materials reduces the grade.
- Handle: A subjective assessment of the wool's feel, including its softness, elasticity, and loft.
Common Wool Grading Systems
Globally, several systems are used to grade wool, each with its own methodology:
-
Micron System:
- Description: This is the most prevalent and objective system, directly measuring the average diameter of the wool fibers in microns using specialized equipment.
- Advantage: Provides precise, scientific data, making it highly reliable for international trade and quality control.
- Usage: Dominant in modern wool markets worldwide.
-
Bradford Count System (Spinning Count):
- Description: An older, more subjective system originating in England, it estimates how many "hanks" (a hank is 560 yards) of yarn can be spun from one pound of clean wool. A higher count indicates finer wool.
- Advantage: Historically useful for predicting spinning performance.
- Usage: Still used in some traditional markets and as a reference alongside micron values.
-
American or Blood System:
- Description: An historical system developed in the United States, it relates the fineness of wool to the percentage of Merino blood in the sheep. For example, "Fine" wool was historically from purebred Merino sheep, while "1/2 Blood" wool came from sheep with approximately half Merino heritage.
- Advantage: Simple to understand based on breed lineage.
- Usage: Largely obsolete for commercial grading but sometimes used for historical context or by hobbyist sheep breeders.
Understanding Wool Grades: A Comparative Table
The following table provides a general overview of how different grading systems correlate with fiber diameter and common uses. It's important to note that specific ranges can vary slightly.
| Grade Description | Micron Range (µm) | Bradford Count | American (Blood) System | Common Usage |
|---|---|---|---|---|
| Superfine Merino | < 18.5 | 80s+ | Fine | Luxury apparel, next-to-skin base layers |
| Fine Merino | 18.6 - 20.5 | 70s - 80s | Fine | High-quality apparel, activewear |
| Medium Merino | 20.6 - 22.5 | 64s - 70s | 1/2 Blood | Everyday apparel, knitwear |
| Strong Merino | 22.6 - 24.5 | 60s - 64s | 3/8 Blood | Outerwear, durable knitwear |
| Fine Crossbred | 24.6 - 28.5 | 56s - 60s | 1/4 Blood | Blankets, industrial yarns, some apparel |
| Medium Crossbred | 28.6 - 32.5 | 48s - 54s | Low 1/4 Blood | Carpets, upholstery, durable fabrics |
| Coarse Crossbred | > 32.5 | < 46s | Common/Braid | Rugs, felts, insulation, industrial applications |
Note: The Bradford and American systems are less precise than the Micron system and are often used as historical or complementary references.
Why is Wool Grading Important?
Accurate wool grading is critical for several reasons:
- Market Value: Finely graded wool commands higher prices due to its versatility and demand for luxury textiles.
- Processing Efficiency: Graded wool ensures that consistent fiber types are processed together, optimizing machinery settings and reducing waste.
- Product Quality: Proper grading ensures that the right wool type is used for its intended purpose, leading to high-quality, fit-for-purpose end products.
- Producer Feedback: Grades provide valuable feedback to sheep producers, helping them improve breeding and management practices to meet market demands.
For more detailed information on wool grading standards, you can refer to resources from organizations like the USDA Agricultural Marketing Service or the International Wool Textile Organisation (IWTO).
