John Brown discusses the concept of "Book" in the Bible and antiquity; notes that ancients used to write records on metal such as lead and copper.
John Brown, A Dictionary of the Holy Bible (London: Thomas Tegg, 1824), 140
BOOK, a written register of events, or declaration of doctrines and laws. Gen. v. 1. Esth. vi. 1. The books of Moses are the most ancient in the world: nor does it appear that any were written before them. Josephus says, the children of Seth, before the flood wrote their discoveries in arts, in astronomy, and other sciences, upon two pillars; the one of stone to withstand a deluge; and the other of brick, to endure a conflagration; but the obscurity of his narrative, and the want of concurring evidence, render his account very suspicious. The book of Moses are called, the book of the law; and a copy of Deuteronomy, if not of the whole of them, was laid up in some repository of the ark. Deut. xxxi. 25. Men used anciently to write upon tables of stone, lead, copper, wood, wax, bark, or leaves of trees. Hesiod's works were written on tablets of lead; the Roman laws on twelve tables of brass; Solon's on wood: and those of God on stone, probably marble. In very ancient times the Persians and Ionians wrote on skins.