A review by Anjalika Balasingam
Conclusion
There is no objective definition of a contaminant medullated wool fibre that can be substantiated by published trials. The American Society of Testing Materials (ASTM) has published a definition in ASTM-D 2968-89 that uses the ratio of medulla to fibre diameter to define contaminant medullation. But we have been unable to locate references to a trial or trials that substantiate this value. Hunter et al. (1996) reported a trial in which experienced mill staff visually detected objectionable medullated fibres of samples in air. The medulla to fibre diameter ratios of the detected fibres ranged from 0% to 90%, indicating that, either the detection method was unreliable or that the medulla to fibre diameter ratio is an inappropriate parameter to define objectionable medullation. However, when testing mohair in benzyl alcohol, Smuts and Hunter (1983) appeared to support the ASTM definition, although the ratio they found was 0.55 compared to 0.60 for ASTM-D 2968-89. OFDA technology has a definition of objectionable medullated fibres based on fibre opacity and diameter, but this definition is not applicable to bulk presale core testing. Other techniques for medullation measurement such as projection microscope (pm) and the WRONZ Medullameter use the ASTM definition to directly (pm) or indirectly (Medullameter) to specify a threshold level of medullation for contamination.
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