What is a retest?

The term retest is often used interchangeably in two quite different contexts, and this can be confusing.

Some IWTO Specifications (test methods) such as IWTO-19 (Determination of Wool Base and Vegetable Matter Base of Core Samples of Raw Wool) and IWTO-12 (Measurement of Mean and Distribution of Fibre Diameter using the SIROLAN_LASERSCAN Fibre Diameter Analyser) require testing of replicated subsamples. When testing is completed the results of the individual subsamples are compared and if the maximum differences are within specified ranges the results are all combined and the average of all subsamples is issued on the Certificate. If the specified range is exceeded then additional subsamples drawn from the residual sample material and these are remeasured, with specified range checks being applied to all subsamples. This cycle can in some cases be repeated up to 3 times. Sometimes the testing of additional subsamples within a laboratory before the Certificate is issued is referred to as a retest.

However, the correct usage of the term is in connection with a set of measurements made, in accordance with the relevant test method, on a further sample of raw wool drawn from a delivery for which the original Certificate is in doubt. This differs from a recore check test in that duplicate core samples are drawn for possible testing by 2 separate Test Houses to resolve a disputed result. Such sample material must be obtained by resampling and reweighing all bales in accordance with the relevant IWTO Regulations.