A simple check of dye stability in which a damp towel or cloth is left lying on the pile of a rug for several minutes and then examined for transferred color. Hand-knotted rugs colored with natural dyes typically show little or no bleeding, whereas hand-tufted and machine-made rugs colored with chemical dyes tend to start running, so the result serves as one clue among several to whether a rug is authentic. Even a genuine rug can bleed after a careless wash or an unattended spill.