Variable fleeces have fibre diameters that are spread out over a large
range (as opposed to uniform fleeces that have fibres diameters contained
within a much smaller range). This variability can be seen by visual
examination but histogram testing provides more accurate information about
the variability found in the fleece. The histogram patterns (graphs) from highly variable fleeces are much
more spread out than the patterns from the more uniform fleeces. Double
coated fleeces are just one type of variable fleece and these may show a
distinctive pattern in the graph.
Again, there can be fine (low AFD) variable fleeces and coarse (higher
AFD) variable fleeces. A highly variable fleece shows a higher SD, such as 7
microns and up. The CV is also higher, around 30 % and up. Of the histograms
from midside submitted to the Great North American Histogram Contest, 31 or approx. 41%, show either highly
variable or double coated characteristics. 7 of the histograms also had AFD’s over 30 microns (30 microns and up being the diameters that cause itch
or prickle for most people).
A histogram from a highly variable fleece has a shape more like a mound
or a hill than a tower or peak, often with a longer tail to the right
representing the coarser fibres. Keep an eye on the scale of the numbers on
the bottom of the graph. The number where this tail ends varies from graph to
graph and it is important to know if that coarsest measurement was 66
microns or 91 microns.
A distinctly double coated fleece may show two mounds or two small towers
or one taller tower and a much lower mound off to the right. If the two
shapes are close together on the graph, the difference in diameter between
the coats is small. If the shapes are farther apart, the difference in
diameter is more pronounced. A double coated fleece with very little
difference in fibre diameter may not show two distinct shapes. Instead, they
can overlap, giving the pattern an almost flat top or plateau.
Many double coated fleeces that have only a small difference between the
fibre diameters of the different coats may not be recognized as double
coated. This can occur in fine, medium and coarse fleeces. Often, the degree
of variance is small enough that the two coats can be processed together
without a significant decrease in the quality of the resulting product.
The double coats that have a large difference in their AFD’s (the mound shapes
are quite a ways apart on the graph) may need to be separated by hand and
processed individually to get the best use out of the fleece. Icelandic type
fleeces are a good example of this.
Some double
coats have the majority of the fibres in the micron range of the finer coat
with just a small percentage making up the coarser coat (sharp peak or tall,
flatter topped tower with a much lower mound off to the right).
Some double
coats have a more even distribution of fibres between the two coats (two
towers , almost the same height or with the one to the right slightly
lower). These ones are generally harder to separate by hand into two
distinct coats for processing. If the fibre diameters in the two coats are
similar, this will not have much of an impact on yarn quality. If they
are quite different, yarn made from the combined coats will not feel as nice
or perform as well.
