Abrash is horizontal, naturally occurring colour variance or hue change. These colour changes usually are due to the weaver using wool dyed in different dye batches. It may appear to be the same colour upon weaving, but over time, the dyes oxidize or fade differently. This is a far more common occurrence in Village and Tribal rugs, where wool is dyed in small batches. These colour variances are not a contributing factor to loss of value in a rug.
This phenomenon is so common in hand-knotted rugs that abrash is often purposely woven into machine-made rugs to make them appear more authentic.
Sometimes the abrash is subtle enough that normal tracked-on soil may camouflage it. If left long enough, rug owners often forget it’s there, only to rediscover it after cleaning.
There is nothing a rug cleaner can or should “do” about abrash. It is unique colouration anomaly that should be enjoyed by the rug owner.