Farm Tech

Wool testing and appraisal can make you money

Making sense of the figures on wool test certificates

Farmers who have had their wool tested and appraised have a sound basis for establishing their selling price. They are in a position to be strong sellers.

Conversely, if buyers are confident about the properties of the wool they are buying, they are in a position to offer their best price.

Growers selling wool privately and through Woolnet (www.woolnet.co.nz) are strongly encouraged to have their wool tested and appraised before offering it for sale.

Test and appraisal results for Woolnet lots are loaded onto Woolnet for buyers to view.

All wool that goes through the auction system is tested for yield, micron, colour and vegetable matter (VM). The first three of these measurements are extremely difficult to assess by eye and touch, which may have a big influence on the value of wool.

Samples for auction lots are also appraised by buyers at the auction-selling centre during the three days before a sale.

Appraisal involves assessment by eye and touch of a sample for characteristics which cannot be easily, reliably or economically measured using standard tests. Bulk, lustre, visual colour, length and strength in crossbred wools are some of the characteristics appraised.

Appraisal

Meat & Wool Innovation's appraisers in Napier and Christchurch provide an appraisal service for growers.

In the North Island, phone Napier 06 835 1888, or phone free on 0800 4 496 657 (North or South Island).

Commonly certified tested measurements

Yield

Yield is the weight (or proportion) of clean wool after the removal of impurities, expressed as a percentage of the greasy wool weight. It is a significant factor in wool trading because it is used to estimate the quantity of usable fibre in a lot.

There are a number of commercial yields calculated during testing, but the IWTO Schlumberger Dry Top and Noil Yield is the standard trading yield used in New Zealand, and is the yield measurement used in Woolnet.

Vegetable matter

Removing vegetable matter during initial processing reduces yields because it becomes entangled with fibres. Vegetable matter can cause yarn breakage and irregularity, and it spoils both the handle and appearance of fabric.

As vegetable matter is not readily taken out of wool during scouring, it is a significant factor buyers consider when purchasing wool.

Diameter

Fibre diameter is the main determinant of spinning limit (i.e. the minimum number of fibres in a cross section that will permit a yarn to be spun), and consequently spinning efficiency. It is also a major determinant of the handle (or ‘comfort factor’) of wool and affects the products it could go into, for example, worsted, knitting or carpet yarn.

Fibre diameter also influences dyeing performance, with fine fibres dyeing to a much deeper shade than stronger fibres in both yarn and product form.

As a result of its importance to processing, fibre diameter is a major determinant of the price of wool traded on the world market.

Length

Fibre length also has a very important effect on yarn regularity, strength and extensibility, which in turn influence subsequent manufacturing efficiencies, product qualities and performance.

Fibre prices normally reduce as length decreases, especially for fine and medium wools.

Length and strength

Tenderness in wool is caused by a reduction in fibre diameter at some point. Length and strength testing is primarily used for fine apparel wools.

Length after carding

This test for crossbred scoured wools simulates commercial processing conditions and shows a processor how a parcel of wool may perform in their plant.

Colour

Good colour is extremely important for yarn or fabrics that are to be dyed to pale pastel shades. The whiter the wool, the greater the range of dyeing options available. Also, the natural yellow component of wool is not always light stable, so pale colours dyed on yellow wools may fade quickly.

Poor wool colour may also indicate the presence of other processing faults, such as tenderness.

In general, finer wools are brighter and whiter than stronger crossbred wools. Some types of discolouration can be removed by scouring, others cannot.

Test Houses

Wool can be tested in New Zealand at two accredited commercial test houses: The NZ Wool Testing Authority Ltd in Napier, and SGS Wool Testing (www.sgs-wts.com) in Wellington.

Links

SGS Wool Testing – www.sgs-wts.com
Woolnet – www.woolnet.co.nz

Deciphering the test certificates

Description of information found on NZ Wool Testing Authority test certificates

IWTO Test Certificate:
A certificate produced in accordance with the regulations and specifications of the International Wool Textile Organisation (IWTO).

Farm Brand:
The farm identification under which the wool is sold.

Quantity:
This is the number of bales in the lot, and more importantly, the gross mass, declared tare and the nett mass of the lot at the time the core samples were drawn.

Colour:
The colour result is measured on clean processed wool fibre and is represented by the tristimulus values X, Y, Z. The Y value is an indicator of the wool brightness and the difference between Y and Z (Y-Z) represents the level of yellowness. If the Y value is high the wool will be bright, but if it is low, the wool will appear dingy. If the value of Y-Z is low, the wool will be white, but if it is higher the wool will be yellow.

Length/Strength:
Mean Staple Length: The average length of the measured staples in millimetres.

Coefficient of Variation of Staple Length: An expression of the variation in the length of the staples. The smaller this value is, the more uniform the length of the staple.

Mean Staple Strength: The average strength of the measured staple reported in Newtons per Kilotex. The measurement represents the average amount of force required to break a staple of standard thickness.

Distribution of Position of Break: Whether a staple is weak or sound, it is broken during the strength test. The proportion of the staples which break in the tip, middle or base region are expressed as a percentage. This measurement is important in predicting the length of processed wool.

Test Number:
NZWTA Ltd’s unique identification for the test certificate.

Wool Base:
The dry weight of wool fibre free from all impurities (e.g. vegetable matter, moisture, dirt, grease, etc.) expressed as a percentage of the weight of the greasy core sample. Wool Base is used in the calculation of commercial yields. IWTO-19 is the International Wool Textile Organisation's Standard test number 19 for measuring wool base.

Vegetable Matter Base:
The dry weight of vegetable matter (VM) expressed as a percentage of the weight of the greasy core sample.

Hard Heads/Twigs:
A component of Vegetable Matter Base. It includes large hard burrs covered in readily removed spines. Hard Head/Twigs do not contribute to loss of wool during processing.

Calculated Commercial Yields:
IWTO Scoured Yield at 16% Regain: IWTO Scoured Wool is calculated from Wool Base, and includes VM. Standard residual grease and dirt allowances are made and 16% moisture regain is included in the yield. The yield estimates a “washing yield”, i.e. the yield of product after scouring but before any processing occurs to remove VM.

IWTO Schlumberger Dry: IWTO Schlumberger Dry Top and Noil Yield is the most common commercial core test yield and predicts the amount of top and noil that can be combed from greasy wool. In calculating the yield a varying allowance is made for processing losses, depending on the amount of VM in the lot.

Woolnet uses the IWTO Schlumberger Dry yield as the basis for all business as it is generally accepted as the best indicator of performance for New Zealand wools.

Fibre Fineness:
Mean Fibre Diameter: The average diameter of the fibres in a sale lot measured in microns (micrometres) using the Airflow apparatus or OFDA/Laserscan technology.

Coefficient of Variation: The coefficient of variation of a range of wool fibres. All wool fibres vary in diameter as a result of changes in season, environment and animal health. CV helps describe this variation and so helps the processor determine processing performance.

Medullation: Medullated fibres are thick, hollow, hair-like fibre that do not take dyes and show up white in the final product. This figure is the percentage of medullated fibre in the greasy core sample.

Fibre Curvature: A way of measuring the crimp of wool fibres, and measures how much fibre bends along a short length of wool. Values range from 50 to 150 degrees per millimetre. Lower figures are associated with increased processing efficiency and sleeker, softer fabrics with greater depth of yield shade after dyeing.

Deciphering the test certificates

Description of information found on SGS test certificates

[Insert thumbnail image of SGS test certificate, linked to full-sized image.]

Iwto Test Certificate:
A certificate produced in accordance with the regulations and specifications of the International Wool Textile Organisation (IWTO).

Test Number:
SGS’s unique identification for the test certificate.

Identification:
It is essential that the bales certified are clearly identified. This information can include the farm brand, bale IDs, the broker, and sale centre and sale date in the case of wools going to auction.

Quantity:
This is shown by the number of bales in the lot, and more importantly, the gross weight, declared tare and the nett weight of the lot at the time the core samples were drawn.

Wool Base:
The dry weight of wool fibre free from all impurities (e.g. vegetable matter, moisture, dirt, grease, etc.) expressed as a percentage of the weight of the greasy core sample. Wool Base is used in the calculation of commercial yields.

Vegetable Matter Base:
The dry weight of vegetable matter (VM) expressed as a percentage of the weight of the greasy core sample.

Hard Heads/Twigs:
A component of Vegetable Matter Base. It includes large hard burrs covered in readily removed spines. Hard Head/Twigs do not contribute to loss of wool during processing.

Calculated Commercial Yields:
IWTO Scoured Yield at 16% Regain: IWTO Scoured Wool is calculated from Wool Base, and includes VM. Standard residual grease and dirt allowances are made and 16% moisture regain is included in the yield. The yield estimates a “washing yield”, i.e. the yield of product after scouring but before any processing occurs to remove VM.

IWTO Schlumberger Dry: IWTO Schlumberger Dry Top and Noil Yield is the most common commercial core test yield and predicts the amount of top and noil that can be combed from greasy wool. In calculating the yield a varying allowance is made for processing losses, depending on the amount of VM in the lot.

Woolnet uses the IWTO Schlumberger Dry yield as the basis for all business as it is generally accepted as the best indicator of performance for New Zealand wools.

Fibre Fineness:
Mean Fibre Diameter: The average diameter of the fibres in a sale lot measured in microns (micrometres) using the Airflow apparatus.

Colour:
The colour result is measured on clean processed wool fibre and is represented by the tristimulus values X, Y, Z. The Y value is an indicator of the wool brightness and the difference between Y and Z (Y-Z) represents the level of yellowness. If the Y value is high the wool will be bright, but if it is low, the wool will appear dingy. If the value of Y-Z is low, the wool will be white, but if it is higher the wool will be yellow.