Section 2.76: Consistency or Uniformity

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Consistency or Uniformity

Uniformity and consistency are frequently found in highly organized fleeces, and highly organized fleeces are often very fine. Generally, a finer fleece, in terms of AFD, has fewer thick primaries. Uniformity frequently produces a soft, silky feel. While no relationship between fineness and frequency or style of crimp has been established, good definition of crimp is usually related to uniformity. Fleeces with well-defined crimp structure throughout, tend to be finer than those that lack well expressed crimp.

Many breeders particularly value an alpaca that exhibits a very low Coefficient of Variation (CV) in its histogram. In fact, low CV is sometimes felt to be a more important indicator in choosing breeding stock than the AFD (average fineness) value. In truth, it is the interplay of these two values that is particularly telling. What breeders really want is to produce stock that exhibits both low AFD and low CV. In other word, breeders hope to produce alpacas that have uniformly fine fiber, not just a low average fineness. Consistency has tremendous implications for the quality and value of finished yarns and textiles. 

When evaluating the measurements provided by a histogram, many breeders and fleece experts focus on the "coefficient of variation" (CV), rather than the standard deviation (SD). SD values increase as AFD (also known as the "mean fiber diameter" or "MFD") increases. The CV is a more precise gauge of uniformity because it expresses the ratio of SD to AFD, which some testing labs report as a percentage (SD expressed as a percentage of AFD). The formula used is: CV = (SD ÷ AFD) x 100. Therefore, where AFD is 16.0 and SD is 3.0, CV = (3.0 ÷ 16.0) x 100 = 19 %. Fleeces that have CVs lower than 20% are very uniform, with the very best animals, in terms of fleece consistency, having CVs in the mid- to low-teens. 

The following two histograms illustrate the usefulness of focusing on CV, rather than SD when gauging uniformity. These two alpacas have very different AFD and SD values, but they have nearly identical CVs. This tells us that, despite the highly different SD numbers, the two alpacas are almost equally consistent, even though one is much finer overall. 

Alpaca #1: AFD: 21.0 microns; SD: 4.4 microns; CV: 21.1%; >30 microns: 2.7%.

Alpaca #2: AFD: 36.6 microns; SD: 7.9 microns; CV: 21.5%; >30 microns: 83.1%.

Consistency and uniformity do not apply only to fiber diameter. They are also considerations when it comes to color and fiber length. Textile producers need fiber of equal length in order to produce good end products. As previously discussed, variable length fibers contribute to a "prickle factor" for the consumer. With respect to color, commercial textile manufacturers generally require that there be no color "contamination" – white must be white, with no other colors mixed in, black must be black, and so on. Nonetheless, a good market has developed for fleeces that exhibit a combination of colored fibers, as do most fawn and gray alpacas. When well blended, these color combinations produce unique and valued results. Some processors may, in fact, blend pure black alpaca with white alpaca to achieve a nice mix that appears gray in the finished product. As our herds of colored alpacas grow, so too will the markets for a wide variety of uniquely natural colors.

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