Generated illustration: an indigo source leaf and processed dye cakes.
A deep blue natural dye, traditionally obtained from Indigofera plants and named alongside madder root and walnut husks among the plant dyes that color the wool of natural-dye rugs. It provides the deep midnight blues of rugs such as Heriz and Bakhtiari, and the dyed yarn reveals its full blue only as the dye oxidizes in air. In rug descriptions the word also names that deep blue shade itself.
The root of the madder plant (Rubia tinctorum), a natural red dye and the source of the terracotta tones in Persian and Oriental rugs. Together with indigo and walnut husks it is among the plant dyes used to color the wool, bonding to its natural lanolin. Slight shade variations within one color area, known as abrash, are normal in rugs dyed this way.
Colorants extracted from plants, seeds, flowers and roots and, in some traditions, from animal sources, used to color rug wool and silk. Weavers, above all tribal weavers, often prepare them from local plants and other natural resources of the region, which helps give each region its characteristic tones; madder root (terracotta reds), indigo (blues), walnut husks (browns) and pomegranate rind (yellows) are typical dyestuffs. Because dye is made in small artisanal batches, shades differ slightly from batch to batch, producing abrash. Natural dyes are prized for rich, harmonious, mellow color that fades gently and evenly with age and bleeds little on a damp cloth, though a rug may combine mostly natural dyes with a few synthetic ones.
The outer skin of the pomegranate fruit, a plant dyestuff used for the yellows in naturally dyed rugs, alongside madder root for reds, indigo for blues and walnut husks for browns.
The green outer covering of the walnut, a traditional plant dye for brown wool. Rug dyers boil it to obtain deep brown to umber shades, and it belongs to the same vegetable palette as madder root (terracotta reds), indigo (blues) and pomegranate rind (yellows). Plant dyes of this kind are what separate traditionally dyed rugs from those colored with synthetic dyes.