A few centuries back, almost all Persian rugs were produced by nomadic tribes almost entirely with locally obtained materials, wool from the herds and vegetable dyes, or other natural dyes from the land. They used geometrical designs that varied from tribe to tribe, most famous are the Yomut, Ersari, Saryk, Salor and Tekke. Irregularities, considered part of the charm by many rug collectors, were fairly common since natural materials varied from batch to batch and woolen warp or weft may stretch, especially on a loom that is regularly folded up for transport and set up a new at another camp. More recently, large rug workshops in the cities have appeared, there are fewer irregularities, and the technology has changed somewhat. Designs have evolved, but traditional motifs still dominate.