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.
Wool left in its natural fleece colors, with no dye applied, so its shades run only through white, cream, brown, gray and black. Weavers combine white and black wool to reach these tones, which is how natural Gabbeh rugs, usually on a cream ground, get their palette. Many cream grounds in Persian and Oriental rugs also contain undyed wool; these areas can show slight variations of tone that shift as the rug ages, which is normal and not a defect.