A New Test for Wool

April 2016

The NZ Wool Testing Authority has added new test for wool staple length and strength

Objective testing of staple length and strength in crossbred wool has been developed, verified and introduced by NZ Wool Testing Authority. Independent objective assessment gives all sectors of the industry greater confidence to value wool to its true potential. It is now being offered as a commercial test to growers to enhance the measurement and marketing of their wool and included in the profiling of clips and lots by independent wool brokers based in Hawke’s Bay. The procedure concentrates on length because it is one of the most important attributes of wool.

Length is used to describe crossbred wool and the prices paid to the wool grower vary according to the length. However, despite the widespread use of objective measurement throughout the strong-wool industry, length remains the one key characteristic which is still assessed or appraised subjectively, both visual and by touch. The risk involved is reflected in the valuation.

Objective measurement of length and strength has been carried out on Merino wool for decades and the same principles can be applied to crossbred wool. New Zealand produces the largest volume of crossbred wool for manufacturing purposes (about 90% of the national clip) and therefore the development and proving of the new staple length test creates more value for the NZ wool sector.

The new length and strength test process starts with grab sampling in the wool store, then proceeds to tuft sampling, through staple preparation to actual machine measurement for length and strength and the break point along the staple. Measurements are provided for staple length (SL) in millimeters, coefficient of variation of staple length (CVL) in percentage terms, staple strength (SS) in newtons/kilotex, and the position of break (POB) in percentage of staples breaking at the tip, middle and base regions.

Staple length is presented as an average value rather than a broad range. That means longer wools within a certain traditional description (e.g. 3 to 4 inches) should receive the premium value they deserve. Also the overlapping of lengths between traditional descriptions may mean that some appraisers would have conservatively under-valued (e.g. called 2 to 3 inches by some appraisers and 2 to 4 inches by others). By using an average length, all appraisers can value it using the same measurements.

Low staple strength would indicate tenderness in the wool caused by environmental conditions during the growth of the fleece. Weaker wool may lead to fibre breakage and loss during processing. This aspect of the new test has been the focus of more research work at NZWTA.

NZWTA has not yet advertised a price schedule for length and strength testing of crossbred wool but advises that the cost of a test conducted on the average lot size of 13-15 bales would average out at 1 to 1.5c/kg, which it says would be recovered by the grower in the premiums paid for objectively testing wools. Depending on market conditions throughout the year, there can be up to 50c/kg difference between adjacent length descriptions.

The benefits of objective testing of staple characteristics are spread through the wool value chain, ultimately maximising the return to the wool grower. The grower has confidence that buyers’ assessments are accurate, that it reduces the need for a risk margin, provides information for farm management decisions, increases competition from buyers, and captures the value that may be lost if characteristics are underestimated.

For the brokers it provides sound data for shearing and wool handling advice, enables clear market signals, and ensures maximum value for wool growing customers.

For wool exporters it raises confidence in bidding, allows more accurate prediction of processing performance, reduces the risk of appraisal errors, and reduces the risk of claims.

For wool processors it allows the specification of wool in precise, objective terms, helps processing performance to be predicted, enables machinery settings and processing performance to be maximised, and reduces the potential for disputes and claims.

In New Zealand where the sheep population mainly consists of coarse-wool breeds and approximately three-quarters of wool is exported in scoured form, greater emphasis has traditionally been placed on testing the length parameters of commercially-scoured wool. This is conducted using the Length after Carding (LAC) test. The LAC test has demonstrated stability and reliability over two decades and a significant proportion of NZ wool is now exported on the basis of LAC specifications.

Purchasing of greasy crossbred wool is generally based on test data for yield, vegetable matter, fibre diameter and colour. This is accompanied by subjective appraisal of length. More recently, there has been growing interest in staple length measurement to complement the suite of objective tests used to describe crossbred wool.

To be taken up commercially, crossbred wool growers and buyers will need to be convinced of the accuracy, repeatability and profitability.

NZWTA received financial support from Callaghan Innovation to set up and run a trial process using existing equipment and methodology for Merino length and strength testing. It then submitted to the International Wool Textile Organisation that the existing protocols (IWTO-7 and IWTO-30) should be amended to include length testing for crossbred greasy wool. Further work is being performed on the staple strength characteristic as well as the application of length and strength measurement to predict the processing performance of crossbred wool, as measured by the LAC test.