This article examines a little-known and unstudied alchemical treatise, The Epistle on Alchemy (al-Risāla fī l-ṣināʿa) attributed to Aristotle, purportedly translated from Syriac into Arabic by the Nestorian bishop ʿAbdīshōʿ bar Brīkhā (d. 1318). In particular, I investigate the Epistle’s discourse on the concealment and revelation of alchemical knowledge. Like other occult sciences, alchemy was characterised by a marked concern for secrecy and frequently employed codes, or Decknamen, when discussing the “Noble Art.” Yet the author of the Epistle consciously avoids such conventions, choosing instead to disclose its mysteries in an open and accessible manner, while making clear that secrecy would otherwise be necessary were the reader deemed unworthy. By engaging with scholarship in Islamic and Jewish occult science and esotericism, I show that the author of the Epistle navigates the boundaries between concealment and disclosure by framing his treatise as a private exchange between two foundational figures of philosophy and kingship: Aristotle and Alexander the Great. Based on a study of the Epistle’s sources and genre, I consider it possible that the work was not a translation of any Syriac original but a composition by ʿAbdīshōʿ himself and a product of the Arabicspeaking, Islamicate environment in which he lived.