A micron (micrometre)
is the measurement used to express the diameter
The lower microns are the finer fibres.
Fibre diameter is the most important characteristic
of wool in determining its greasy value.
Every fleece comprises a very wide range
of fibre diameters - for example a typical
Merino fleece will contain fibres of
as low as 10 microns in diameter, and there
could be fibres with diameters exceeding
25 microns, depending on the age and health
(or nutrition) of the sheep. What is usually
referred to as wool's "micron"
is the mean of the fibre diameters or average
diameter. This may be measured in a number
of different ways.
Small samples can be taken from the side
or fleece of a sheep and measured using
a portable instrument such as an OFDA2000
(Optical Fibre Diameter Analyser); or a
mobile instrument system called a Fleecescan.
Both these systems have been studied extensively
and used correctly should give reasonably
reliable results. Pre
micron test results are a useful guide for
classers in determining lines of wool to
be made. Samples of fleece can also be shorn
from the animal and sent to a laboratory
for measurement ("midside sampling").
Most fleece-testing laboratories nowadays
use related instruments to those mentioned
- either the OFDA models or the Laserscan.
Merino stud rams are mid-side sampled and
the test results are displayed in the sale
Once the fleeces are baled and prepared
for sale as lots, they are commonly sampled
by coring in the broker store and the samples
sent to certification laboratories. Here
the core samples are cleaned, dried and
prepared for measurement under strict test
methods. Merino wools are normally measured
on Laserscan instruments in Australia, New
Zealand and South Africa, although OFDA
instruments may also be used in some cases
(the results from these two types of instrument
are quite similar). The coefficient of variation of fibre diameter
(CVD) is a measure of the variation in fibre
fineness within the sample fleece, relative
to the average fibre diameter. Crossbred
and coarse wools are often measured for
mean fibre diameter by older instruments
- "Airflow" in many parts of the
world, and even a projection microscope
in some cases.
hogget wool is finer and generally more
valuable than the wool from older sheep.
Most wool between 11.5 and 24 microns in
fibre diameter is made into clothing. The
remainder is used for other textiles such
as blankets, insulation and furnishings.
The finest bale of wool ever auctioned
sold for a seasonal record of 269,000 cents
per kilo during June, 2008. This bale was
produced by the Hillcreston Pinehill Partnership
and measured 11.6 microns, 72.1% yield and
had a 43 Newtons per kilotex strength measurement.
The bale realised $247,480 and was exported