The practice of estimating how old a handmade rug is by weighing several clues together, since no single one settles it. Experts look at wear, the polish of the back, how the dye fades from tip to base, the foundation (rugs woven after the 1930s usually have cotton rather than wool), whether the design fits a particular era or a stage in its locale's style over about 150 years, and whether a supposedly very old rug shows any repairs. Old patterns are copied today, so design alone is not enough.