Generally regarded as the best method for indigo dyeing of yarns. These yarns are twisted together until they form a rope and then briefly dipped in indigo baths.
Because of the short dyeing time, the dye does not fully color the yarns. The resulting ring-dye yarn therefore fades faster than yarn that has fully absorbed the indigo. One of the three main methods to dye indigo yarn, also see ‘Slasher Dyeing’ and ‘Loop Dyeing’.
Source: Nouvelle de Nîmes Nº 5: The Denim Dictionary