Histograms
Histograms are the only reliable method for accurately testing for fibre diameter. Histograms allow fibre diameter and variability to be measured by either the Minicore Method (MCR) or the Butt Cut Method (BC). We use both methods by taking samples from the middle of the side of the animal in the blanket location. The sample must be cut at the skin level and should be a two-inch square in size plus at least two inches in length for the MCR method of testing. The Butt Method (which is used by Yocom-McColl) only tests the fibre diameter at the end closest to the skin. Some people believe this is the better method of measurement as the fibre closest to the skin will be least affected by weather, nutrition, and environment. However, the Minicore Method (also known as the OFDA Test done at Olds College in Alberta, Canada), measures the diameter of the fibre from the skin to the tip so you get an average fibre diameter over the entire year for that specific fleece. One could also determine how certain variables (such as nutrition and environment) effect the fleece as changes in fleece diameter will correspond to these variables throughout the year. Both tests are extremely useful in determining the overall fineness of as animal.

UNDERSTANDING HISTOGRAMS

With Yocom-McColl (BC Method), a histogram will tell you the Average Fibre Diameter (AFD) or Mean, the Standard Deviation (SD), the Co-efficient of Variation (CV), as well as the percentage of fibres greater than 30 microns. The OFDA Test (MCR Method) will give you additional information such as sample size, spin fineness, comfort factor, the percentage of fibres that are above average, the number of medullated fibres, mean opacity, the average diameter of medullated fibres, curve and curve number, as well as the percent of medullated fibres by volume and weight. Some of the measurements are self-explanatory, but below is a description of those that need a little more explaining.

Average Fibre Diameter (AFD) or Mean - the average fibre diameter measured in microns. One micron equals 1/25,400th of an inch.

Standard Deviation (SD) - the amount of variation within a sample. The smaller the SD, the more uniform the population of fibres measured. The more uniform the fibre, the softer the handle. SD generally increases as the AFD increases.

Co-efficient of Variation (CV) - the spread of fibre diameter variation throughout the fleece. It is the SD divided by the AFD (Mean) multiplied by 100, and reported as a percentage. Lower CV values are associated with higher staple strength and will produce more even yarns. As the AFD increases, the CV decreases. Also, a 5% decrease in CV is equal to a one micron decrease.

Sample Size - the number of fibres in the sample tested.

Spin Fineness (SF) - an estimate of the performance of the sample when it is spun into yarn. SF can be improved by decreasing the AFD or the CV.

Comfort Factor (CF) - the percentage of fibres that are under 30 microns. The opposite value (percentage of fibres OVER 30 microns) is given by Yocom-McColl.

Mean Opacity – tells how well the fibre transmits light.

Curve – the degree of curve in a fibre which is a direct correlation to crimp.

Curve Number – the number of fibres in the sample measured for curve.

 
 
 
   
Last Updated ( Friday, 04 July 2008 06:51 )