The bowls are ordinary domestic earthenware, and nothing about them was made for the purpose. What makes one an incantation bowl is that someone wrote on the inside in ink, in a spiral turning outward from the centre, and then buried it inverted under a floor, in a corner, at a threshold or beneath a doorway. The inversion is the point: the bowl is a trap, closed over what it holds.
The texts protect a household against a listed range of dangers. Demons, liliths, the evil eye, curses spoken by named or unnamed enemies, illness, and harm to children and to pregnancy recur throughout. Clients are named, often with a matronymic, which is why the corpus is evidence for the population of Sasanian Mesopotamia as much as for its magic: names in the bowls are Jewish, Christian, Mandaean, Zoroastrian and Persian, sometimes within one household.
They were written in three script traditions in use side by side across the same region and the same centuries, Jewish Babylonian Aramaic in square Hebrew letters, Syriac, and Mandaic. The formulary crosses between them. That is one of the most interesting facts in the corpus, because it means practitioners of different religious communities were drawing on shared material at a level where their communities were otherwise distinct.