Reading a palimpsest's erased lower text has always meant fighting the very process that was supposed to remove it. A medieval scribe scraping parchment clean rarely succeeded completely, and faint traces of the original ink often survive under the newer writing, visible at an angle, under strong light, or not at all to the unaided eye. For Codex Ephraemi Rescriptus, the breakthrough came in the 1840s from the German textual critic Constantin von Tischendorf, already on his way to becoming one of the towering figures of nineteenth century biblical scholarship, who applied chemical reagents directly to the parchment to darken the faded original ink relative to the page.
The method worked, recovering readable biblical text that earlier scholars, working by eye alone, had been unable to reconstruct with confidence, and Tischendorf's edition of the lower text became the standard scholarly reference for generations. It came at a cost modern conservators regret: the reagents Tischendorf used are now understood to have caused chemical damage to the parchment, staining and weakening pages in ways that make some passages harder, not easier, to read using today's non-invasive imaging techniques. The manuscript that gave textual criticism one of its earliest chemical recovery successes is also, by modern conservation standards, a cautionary example of a good result achieved by a method nobody would use again.