Subtle shifts in color within a handmade rug, often visible as horizontal bands across the field. They arise because successive dye batches never match exactly, because differences in the wool's fat and oil content make colors change unevenly with age, and, in cream areas woven from undyed wool, because the fiber changes tone as it ages. Abrash often grows more distinct with age, so in an older rug it counts as a sign of natural dyes and hand production rather than a fault, while a newer rug is still checked for even color. Machine-made and some new hand-knotted rugs imitate it on purpose.
Dye that has migrated from one colored area of a rug into the neighboring areas, for example after a professional wash or after a liquid spill that was not properly dealt with. Older rugs that have been washed several times are checked for it in particular. A rug with no color run commands the best price, while a significant run is a serious flaw that can rule a rug out at inspection. It is damage, unlike abrash, the natural shade variation of handmade rugs.
A single batch of dye, together with the yarn colored with it, all of which takes the same shade. Natural dyes are made in small artisanal batches, and when one runs out the replacement cannot be matched exactly, so yarn from different lots differs slightly in tone. In a finished rug the difference shows as the color shifts known as abrash, which is read as a sign of hand dyeing, whereas a perfectly flat, uniform color suggests synthetic dyes and machine making.
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 lightening of a rug's colors after long exposure to direct sunlight, most noticeable when one part of the rug sat in a sunny window patch while the rest stayed in shade, leaving that area visibly paler. Natural dyes soften with age in any case, but patchy fading counts as a condition flaw and is not the same as abrash, the gentle color variation that comes from dye batches and wool. Curtains or blinds at peak hours, UV-filtering film, a piece of fabric laid over an exposed patch and occasional rotation of the rug limit it; a rug sunned outdoors to dry should not have its face left long in strong sun.
Various techniques for coloring carpet yarns, including beck dyeing (immersion in dye baths), continuous dyeing (application after tufting), space dyeing (multiple colors on a single yarn), and solution dyeing (color added to liquid polymer before extrusion). Each method offers different benefits for colorfastness, pattern capabilities, and environmental impact. In hand-knotted rugs the wool is dyed as spun yarn before knotting, with natural dyes from plants, roots, and flowers, which tend to mellow with age, or with synthetic dyes; differences between dye batches are a main source of abrash.
A traditional method of dyeing carpet yarn in which loose skeins (loops) of already spun, plied yarn are immersed in dye baths before the yarn is knotted or woven into the rug. This technique, common in handmade carpets, works in separate batches, and small differences between batches, together with differences in the natural fat of the wool, produce the subtle color variations known as abrash that give traditional rugs their characteristic depth and visual interest. The process is still used by artisans who create custom-dyed yarns for specialty carpets.