Running of Color (“Nijimi”) in Cotton Cloth Tie-Dyed with Natural and Synthetic Indigo

Abstract

The characteristics of the running of color (“nijimi”) were quantitatively analyzed in order to elucidate the difference of natural indigo dyeing and conventional synthetic indigo dyeing. The luminance distribution curves and half-widths of the running of color were evaluated for the clothes tie-dyed with traditional natural indigo and conventional synthetic indigo. A single Gaussian function fits to the profile of the running of color produced by natural indigo reduced by fermentation, while the running of color produced by synthetic indigo prepared with sodium hydrosulfite was approximately represented by a linear sum of two Gaussian functions. The half-width profile of the running of color is in the following order : synthetic indigo ⁄ reduction method (sodium hydrosulfite) > synthetic indigo ⁄ reduction method (zinc powder) > natural indigo ⁄ reduction method (fermentation). The running of color is thus concluded to be due to the mode of indigo penetration into fiber, which depends on dyebath preparation. A critical difference in dyeing process is the speed of reduction of indigo, and could not be attributed to a small amount of impurity contained in natural indigo.