 An example at the Oriental Institute in Chicago was bought from a Cairo art dealer in 1929, and is now thought to be a fake, based in part on the fact that it is made of brown quartzite, a material common to none of the other reserve heads found "in situ".The explanation originally put forward by Ludwig Borchardt, and later expanded upon by other early 20th-century Egyptologists including Junker and Reisner, was that the reserve head served as a ritualistic substitute for the real head of the deceased, in case it was damaged.Another suggestion put forward by Egyptologist Nicholas Millet was that they served as sculptors' prototypes for making further statues and reliefs of the deceased.