FINER THAN FINE
CLASSING YOUR FINE FLEECE
Bob Kingwell (BSc), Monga Alpacas
In the autumn 2012 edition, I introduced you to the Score of Uniform Micron or SUM in an article titled ?Hidden Secrets of the Fleece Histogram? and as you will recall this is obtained by adding the average fibre diameter of a fleece sample (FD) to the standard deviation of the fibre diameters in that sample (SD). This sum of FD and SD is a score that is measured in microns and has been called the Score of Uniform Micron because the SD is a measure of the uniformity of the fibre diameters in the sample.
This article explains how you can use the SUM to class your fine fleece and in particular to class fleece in the ultrafine range to a higher standard than is currently being achieved.
There are several ways of classing fleece. Wool is usually classed by qualified wool classers who rely on their experience based on the look and feel of a fleece to determine which bale it should go into. This is a subjective method that relies on the experience of the classer to make the correct decisions.
A far more consistent and reliable method of classing is to grid test each fleece to determine its suitability for a particular bale. This is a popular method that has been used in Australia to class alpaca fleece since there are currently no qualified alpaca fleece classers and because there is a general lack of alpaca experience amongst wool classers.
Although this is an objective method, it is still necessary to determine which measurements from the grid test are going to be used. Until recently most alpaca fleece was classed only on the basis of its FD since this was the measurement that determined the price paid per kilogram. In the wool industry buyers usually have a number of bales of a particular FD to choose from and it is therefore necessary to use other measurements as well to determine the preferred bale. This unfortunately is not the case for alpaca fleece. Even though there are currently about 150,000 registered alpacas in Australia, the industry struggles to put together just one bale of ultrafine fleece each year.
It became apparent a few years ago that classing fleece only on the basis of its FD was producing bales that did not have the uniformity of fibre diameter to compete successfully with other exotic fibres. These bales often contained unacceptable levels of medullated fibres that were downgrading the more uniform fleeces in the bale. To overcome this problem the comfort factor measurement (CF) was added to the FD requirement for classing. This year the Ultrafine Bale Scheme requires that fleece must have an FD no higher than 19μ and a CF not less than 99%.
USING THE SUM
You will recall in the Autumn article that there is a strong correlation between the SUM and the CF, particularly when the SUM is less than 26. This means that the SUM could be used instead of the FD and CF to class these fleeces. A bale made up of fleece that had a SUM no greater than 23 would be similar to a bale made up of fleece with an FD no higher than 19μ and a CF not less than 99%.
The industry is now starting to produce a significant amount of fleece with a CF of 100%. This year our own fleece herd of 89 alpacas with a CF of at least 95% produced 22 fleeces with a CF of 100%. This is a quarter of the herd. Admittedly most of these fleeces were first and second year fleece but three of them were fourth year fleeces and one was a 6th year fleece.
So how to grade fleeces when they all have the same comfort factor of 100%? When some have lower fibre diameters but higher standard deviations how do you decide which is the most desirable fleece; assuming of course that all other factors are similar? Will it be the one with the lowest fibre diameter or should the standard deviation also be considered?
The Score of Uniform Micron provides an answer to this question since, as I explained in the first article, the SUM takes over when the CF is 100%.
If two fleeces each have an FD of 17μ and one has an SD of 3μ and the other an SD of 4μ they will probably both have a CF of 100%. However the first fleece with a SUM of 20 will contain less medullation than the second fleece with a SUM of 21. For the first fleece, the coarsest 5% of fibres will generally be above 20+3=23μ and for the second, above 21+4=25μ. Remember from the first article that the CEM is approximately equal to SDx2 so that the SUM+SD is approximately equal to FD+CEM. Therefore if the extent of medullation is an important consideration in determining demand, then a bale with a CF of 100% will contain less medullation if it is made up of fleece selected for its SUM rather than for the FD and CF.
The SUM can also be used to estimate just how fine, uniform and free of medullation a bale could be produced by the industry. If a bale has a SUM of 26, its CF will probably be above 95% and the extent of medullation will be acceptable for most applications since no more than 5% of fibres will be over 30μ even though a few of these may be fully medullated. The FD will probably be between 21 and 23μ and the SD between 3.5 and 4.5μ. If the bale FD is 22μ, the CEM will be 30-22=8μ and the SD will be about 8/2= 4μ. Alternatively the SD will be 26-22=4μ.
On the other hand, if a bale has a SUM of 21, the CF will generally be 100% and few if any fibres will be over 30μ and probably none will be fully medullated. The FD will probably be less than 18μ and the SD between 3 and 4μ. If the bale FD is 17.5μ, the SD will be 21-17.5=3.5μ and there will still be 5% of the coarsest fibres above 21+3.5=24.5μ and these fibres will have some degree of medullation.
For a bale to have no medullation, ALL the fibres would have to be less than about 20μ, which is probably not achievable. Even if the FD was 14μ, and the SD was 2.5μ, giving a SUM of 16.5, the coarsest 5% of fibres would still be above 16.5+2.5=19μ and a large proportion of these fibres would be over the 20μ limit.
These are impressive requirements for FD and SD and there would not be too many breeders producing fleece of this quality and none producing any quantity. It does however indicate just how far the industry would have to go if it was to eliminate medullation from alpaca fibre.
It is suggested that a more realistic target might be the commercial production of fleece with a SUM of about 19. The bale FD would probably be between 15.5 and 16.5μ with an SD between 2.5 and 3.5μ. In this case, if the bale FD was 16μ, the SD would be 3μ and 5% of the coarsest fibres would be above 19+3=22μ. Small quantities of this quality are currently being produced which suggests that this would be a commercially achievable goal.
If reduced medullation is an industry priority then it is suggested that greater attention be given to the comfort factor and the coarse edge micron in breeding programs and that when the CF is greater than 95%, consideration be given to replacing it with the Score of Uniform Micron and using SUM+SD to estimate the extent of medullation.
It is only a matter of time before commercial quantities of fleece with a SUM of 19 are being produced. It is therefore suggested that breeders start using the SUM to grade their fine alpacas and to measure the progress of their breeding programs. The FD on its own is no longer adequate and when the CF is 100%, the only way to continue grading performance is to use the SUM.