The more uniform styles of fleece can be fine, medium or coarse. The
defining feature is that the majority of the fibres in the sample are quite
similar in diameter. This can be seen by visual examination but objective
measurement by histogram testing gives a better assessment. In more uniform
fleeces, the SD measurement is smaller; for the more uniform
Shetlands, around 6 microns or under, and the CV is also smaller, around 25%
or under. Using these guidelines, 11 or approx. 15% of the histograms from
midside submitted to the Great North American Histogram Contest represented
more uniform fleeces.
The term "single coated" is used for some of the more uniform Shetland
fleeces. However, even these fleeces do show variability of fibre
diameter. As a comparison, an example of a breed with particularly
uniform fleece is the Cormo, having as much as 90% of its fleece within a 3
micron distribution (Raising Sheep The Modern Way, Paula Simmons,1989, Page
16. The more uniform Shetland fleece histograms show approx. 68% of
the fleece falling within a 9 micron range.
The shape of the histogram of a more single coated or uniform fleece is taller
and narrower than that of a variable fleece. It looks more like a
skyscraper, a sharp peak or a tower and does not show much of a tail
trailing off to the right. This is a visual representation of the larger
number of fibres found within a smaller range of microns. Remember, while the shape of the curve is a great
visual tool, the scale of the graphs is not constant between histograms. The
percentage or number of observations set out on the left side of the graph
may be changed from histogram to histogram to make the graph easier to see.
The spacing of the micron numbers along the bottom may also change. Check
these numbers any time histograms are being compared as it does impact the
shape of the histogram.
In general, the more uniform the fleece, the easier it is to spin it into
a good quality yarn and the better the yarn will perform. Processing a
highly variable fleece (different staple lengths, fibre diameters and crimp
styles) into one yarn is more difficult. The speed of spinning will "throw"
the coarser fibres to the outside of the yarn, causing it to feel more like
the coarse prickly fibres and keeping the finer fibres covered up. The
result is that yarn made from variable fleece is less comfortable for use in
garments, causing more prickle or itch, than yarn made from a more uniform
fleece with a similar average fibre diameter .
A distinct double coat can often be
separated by hand into the finer and coarser coats. Each coat is less
variable than the two together and can be made into a different yarn.
Icelandic type fleeces are often handled this way.
The SF or Spin Fineness on the Natural Fibre Centre histograms is a
measure combining the diameter of the fibres with the variance of the
sample. It estimates the way the fleece will spin. An SF of 23 microns means
that the fleece is estimated to spin as if it had a mean fibre diameter (or
AFD) of 23 microns, even if the actual AFD is 25 microns. The more uniform a
fleece, the lower its SF will be. The more variable a fleece, the higher its
SF will be. This is another useful tool for comparisons.
Again, if you want to use your fleece for garments, enough fineness for
comfort and enough uniformity for good spinning is important. A lower SF (Spin
Fineness) number and a higher Comfort Factor (or a Lower % of fibres over 30
Microns number) will provide these two characteristics.
