Among the Yoruba, twins have special powers much like the orisha and are treated with respect throughout their lives. If a twin dies, the mother seeks a diviner’s advice about which carver should make the ere ibeji to stand in for the dead child. Once the figure is carved, the artist activates it by soaking it in a special solution and rubbing it with specific oils. The mother treats the ere ibeji as if it were alive, feeding, dressing, and bathing the image. Its face is washed with soap or sugarcane fiber, then rubbed with a cloth and indigo or laundry bluing. After a period of time, the facial features may be rubbed away.
Source: Cameron, Elisabeth L. (1996) “Isn’t S/He a Doll?”, Los Angeles, UCLA Fowler Museum of Cultural History. page 68