The purpose of this study was to determine the influence of the operators on the soil release operation in the testing for soil resistance and release of textiles, based on the rate of released soil particles and the weight of adhered soil particles. A prototype release equipment was fabricated. Release operations were performed by the equipment and by the operators. The results of the release operation using the prototype release equipment showed that the rate of released soil particles and weight of adhered soil particles were constant values due to the tension applied to the specimen, the composition, the weave structure and the threads. The results of the release operation in which the operators were divided into a training group and a non-training group, showed no difference in weight of adhered soil particles between the groups of operators. Therefore, it was found that the condition of the specimen with soil on it did not differ significantly between the groups. On the other hand, the standard deviation was smaller for the training group than for the non-training group, suggesting that training of soil release operation had the effect of improving the accuracy. A comparison of the prototype release equipment and the operators show that variation was found to be 2 to 4 times greater for the operators than for the prototype release equipment. This suggests that the variability of the specimen with soil on it produced by the operators may be propagated to the grading.

Our laboratory has reported in many papers on the coloration of fiber materials with amino groups, such as wool, silk, and nylon, using the Maillard reaction, i.e., the reaction with sugars. In particular, by using oxides of reducing sugars oxidized by the Fenton reaction, we have succeeded in significantly shortening the coloration time compared to conventional reducing sugars. For example, in the case of d-glucose, it was revealed that its color concentration was increased by about 200 times. Therefore, in this work, leather with low heat resistance was colored using reactions with oxides of reducing sugar and the relationship between the color concentration and mechanical strength was investigated in detail. First, the coloration of chrome-tanned leather was studied using oxides of d-glucose. Similar to the coloration of wool previously studied, the reaction was highly reactive to leather, and the leather could be colored to a dark, almost dark brown color even under the low temperature condition of 40 °C. In addition, the mechanical strength of leather is reduced by hydrochloric acid, a byproduct during the formation of glucose oxide. The concentration of glucose oxide, temperature of the reaction solution, and pH of the reaction solution were investigated in detail in order to darken the leather and control the reduction of its mechanical strength. As a result, not only was it possible to achieve a darker, almost black coloration, but the reaction in an aqueous solution containing a strongly basic glucose oxide produced interesting results in that the mechanical strength of the leather increased compared to that of the leather before treatment.