5.1 Test Method D2968 for the determination of med and kemp fibers by microprojection may be used for the acceptance testing of commercial shipments of wool and other animal fibers, but caution is advised since only a few types of animal fibers have been subjected to interlaboratory tests to ascertain the precision of tests for med and kemp fibers by this test method. Comparative tests as directed in 5.1.1 may be advisable.

5.1.1 In case of a dispute arising from differences in reported test results when using Test Method D2968 for acceptance testing of commercial shipments, the purchaser and the supplier should conduct comparative tests to determine if there is a statistical bias between their laboratories. Competent statistical assistance is recommended for the investigation of bias. As a minimum, the two parties should take a group of test specimens which are as homogeneous as possible and which are from a lot of material of the type in question. The test specimens should then be randomly assigned in equal numbers to each laboratory for testing. The average results from the two laboratories should be compared using Student's t-test for unpaired data and an acceptable probability level chosen by the two parties before testing is begun. If a bias is found, either its cause must be found and corrected, or the purchaser and the supplier must agree to interpret future test results in view of the known bias.

5.2 Knowledge of the incidence of med fibers and kemp fibers in wool and other animal fibers is of importance to manufacturers of woven or knitted fabrics because of the apparent dye resistance and light reflectance qualities of these fibers. This is not to imply that all kemp fibers will resist dye and all med fibers will accept dye normally. In practice, a proportion of kemp fibers will appear normal after dyeing and a proportion of med fibers will appear chalky white after dyeing. From the perspective of visual and aesthetic problems, medullated fibers having an abnormally large diameter and a high degree of medullation are probably the worst kind.