The Pile
Synthetic materials are never used in the pile or foundation of handmade rugs. Wool, silk, or a combination of the two are the traditional materials used. Dyed wool is customarily found in tribal rugs, and depending on the region, will vary in quality. Persian rugs, especially older pieces, have the absolute finest and softest wool while in Turkish and Indian rugs, the wool tends to be coarser.
Most Chinese rugs are made of silk, primarily because China is the world's leading producer of both natural and manmade silk, and also because the Chinese once believed that the use of wool was a barbaric practice.
Today, the finest rugs are made of silk, and the most luxurious Persian rugs may actually feature highlights containing threads of pure gold.
The Foundation - Warp and Weft
The foundation of a handmade rug is made up of strong threads that run the length (warps) and the width (wefts) of the carpet. In Turkish and nomadic rugs, including those from Western Iran, tightly spun undyed wool is used almost exclusively for the warp and weft. The foundations of finer pieces from Persian workshops today are often cotton, and only the very finest rugs in Iran are woven on silk.
The Fringe
At either end of the carpet, the warp may form a variety of fringes. The weaver decides how they will shape the fringes, either by braiding, knotting, or simply twisting it. The type and length of fringes is not a standard characteristic of rugs of the same area and the fringes have nothing to do with the quality of the carpet.
The Dyes
Until the introduction of chemical dyes in the late 19th century, only natural color sources such as fruits, vegetables, bark, roots and fungi were used. Most popular were the madder root used to produce reds, and the indigo plant for blues.
Chemical dyes are more popular today but natural dyes are still common in Persian tribal rugs. Before wool is dyed, it is prepared by scouring in boiling water followed by steeping in a mordant. Next, it's placed in a big pot with the prepared dye and boiled for a few hours. It is then rinsed in water until there is no more running of color.
Although natural colors are fast, they do fade slightly over the course of time when exposed to direct sunlight and alkalis. This fading, however, produces a muted antique look which many people desire, and which cannot be equaled with chemical.