From Tar Valon Library
Da’tsang means “despised one” in the Old Tongue. Those who have demonstrated that they have no honour are made da’tsang. They wear only black robes, and are given useless tasks to do, such as searching through a pile of sand to find a certain coloured grain, or digging holes and refilling them. This sort of meaningless work is meant to shame the da’tsang into regaining their honour. It takes three Wise Ones to pronounce an Aiel da’tsang, by saying “You are da’tsang” (ACoS, Ch. 40).