Ogam is well known as a writing system invented for the Irish language and used extensively for inscriptions on stone monuments across Ireland and Britain between the late fourth and seventh centuries. Although the script has primarily been examined in the context of early medieval archaeology and epigraphy, its long afterlife as an integral part of Irish manuscript culture from the medieval to modern periods has also been acknowledged. The present contribution seeks to add to the existing scholarship on manuscript ogam by discussing the transmission of ideas about the script as a cryptic device into the nineteenth century, with a particular focus on a recently discovered notebook, National Library of Scotland (Edinburgh) Advocates’ Manuscript 50.3.11 (or ‘The Minchin Manuscript’), which consists almost entirely of healing charms written in ogam.