Procedures

Testing was performed using a CSIRO Dark Fibre Detector (DFD). SARDI supplied a prototype DFD to AWTA Ltd for the period of the trial. The procedure is essentially in two parts:

• Detection and classification of the level of darkness, of non-white, fibrous contamination in 0.5g webs of wool using the DFD, as illustrated in Plate 1, and the CSIRO Dark Fibre Scale* (rating levels 5, 6, 7 or 8); and
• Verification of the source of the detected fibres, e.g. fibre type and origin; dyed or naturally discoloured; medullated or not, using a microscope (up to 200x magnification) as shown in Plate 2.

*Note that research has shown that fibres of levels 5 to 8 (inclusive) on the CSIRO Dark Fibre scale are visible in undyed wool fabric (e.g. underwear) and in fabric dyed to light or pastel shades. Fibres of level 5 appear brown and are barely visible using the DFD; level 6 fibres are a darker brown; level 7 fibres are a dark chocolate colour; and, level 8 fibres are black.

Plate 1: Detection and classification. Prototype CSIRO Dark Fibre Detector used by AWTA Ltd.	Plate 2: Verification. Microscopic examination of Dark Fibres extracted from the samples. Note the metal bar added to the microscope stage to accommodate an A4 transparency capable of holding up to 25 extracted fibres.

Two (2) x operators were used at each site. At AWTA Ltd 2 operators worked in tandem to detect, classify and verify the dark fibre counts of each sample. At SARDI the operators detect and classify but the scientist, Malcolm Fleet, performs the verification. The times recorded in the trial for SARDI relate only to the detection and classification phase. The normal SARDI procedures were used in this trial, except for the following:

• A maximum of 10g or a maximum of 50 Dark Fibres (df), whichever comes first, was measured for each sample.
• Mass of sample tested was recorded if fewer than 51 fibres were counted.