Wax tablets were the standard erasable surfacefrom antiquity to the Renaissance: one or more boards, often bound togetherin a codex form, were coated in wax to be inscribed with a stylus then erased forreuse.7 In early modern England one could also purchase pocket-sized writingtablets featuring paper that had been treated so as to offer a rigid writing surfaceon which markings made with the accompanying metal stylus could be erasedwith a little moisture.8 The slate blackboard is also attested in Europe in musicinstruction in the sixteenth century, sized either for group or for personal use(as is still the case today), and was used at least by the eighteenth century in theteaching of astronomy. The sand tray, a board or slab spread with a fine layer ofsand that one inscribed with a stick and could easily erase, was another long-lived medium: used in ancient Babylon and medieval Islam for calculations andin Europe principally for children and artists learning to write or sketch down tothe Victorian period.9 None of these temporary notes have left any traces, exceptthrough extant higher- order notes made from them.