Another problem, says Mohammed Reza Hakami, a Tehran carpet dealer: Carpets become more valuable when people have walked on them. That is one reason rug dealers and some buyers will leave their new rugs on the sidewalk for a few days. But "nobody could ever cover such a big carpet."
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The removal of aniline or chromium colors would appear to make a rug much more valuable; and it will often sell for a much higher price than it is truly worth.
This is a particularly deceptive practice when it comes to changing the entire medallion or border of a rug to make it all light instead of contrasting. The uninformed buyer will end up with a carpet that appears to be very old and rare, when in reality it is a piece from the 20th century that has been radically altered.
In the long run these newly knotted areas will fade or change and be clearly unoriginal. In addition to the color being off, the texture of the wool is often different than the original which has been walked on for 80 years.
http://focus.antiquescouncil.com/articlepage62.php