SHORTAGE OF MATERIALS and contempt for earlier texts have long encouraged scribes to remove writing from a surface, thus preparing it for different words. Plato compared the ruler Dionysius to a biblion palimpseston, in that his tyrant nature revealed itself like imperfectly erased writing. There are still to be seen, among surviving wax tablets, some which contain traces of a former text under a fresh layer of wax. In the early Middle Ages, vellum manuscripts were sometimes washed rather than scraped. In the course of time, through the effect of the atmosphere or other chemical causes, the original writing would to some extent reappear. In the later Middle Ages the surface of the vellum was scraped away and the writing with it. The reading of these examples is thus more difficult. Double palimpsests exist, such as one in which a Syriac text of Saint John Chrysostom, of the 9th or 10th century, covers a Latin grammatical treatise in a cursive hand of the 6th century, which in its turn has displaced the Latin annals of the historian Granius Licinanus, of the 5th century.
To intensify traces of original writing, various chemical reagents have been used with more or less success, though irreparable damage was sometimes the result. Non-destructive examination, such as with black light and photography, often enables the decipherment of obscure texts with no harm to the more modern. No entire ancient work has been found in any single palimpsest, but portions have often been recovered from different books, allowing original texts to be reassembled.