Isidore, Etymologiae 6.9:
On Wax Tablets:
Wax tablets are the material of literature, the nurses of the young, they themselves
Give intelligence to the youth, and the beginnings of their sense,
the study of which the Greeks are said to be the first to have handed down. For the Greeks and the Etruscans first wrote with iron on wax tablets; later, the Romans ordered that no one should have an iron stylus. On this account, it used to be said among the scribes, ‘Don’t cut into the wax with iron.’ Later, it was established that they write in was with bones, as Atta speaking in the Satire,
Let us turn the plough in the wax and draw the furrough with a point of bone.
What is called graphium in Greek is called scriptorium in Latin; for GRAFE is writing (scriptura).
DE CERIS. Cerae litterarum materies, parvulorum nutrices, ipsae (Dracont. Satisf. 63):
Dant ingenium pueris, primordia sensus.
Quarum studium primi Graeci tradidisse produntur. Graeci autem et Tusci primum ferro in ceris scripserunt; postea Romani iusserunt ne graphium ferreum quis haberet.  Vnde et apud scribas dicebatur: ‘Ceram ferro ne caedito.’ Postea institutum ut cera ossibus scriberent, sicut indicat Atta in Satura dicens (12):
in cera mucroneque aremus osseo.
Graphium autem Graece, Latine scriptorium dicitur. Nam GRAFE scriptura est.