The Dee alchemical notebook cipher

Summary

John Dee (1527–1609) was Elizabeth I’s natural philosopher, mathematician and astrologer, and an active alchemist. A surviving notebook (British Library Sloane MS 1902), passed to his son Arthur Dee and thence through several alchemical hands, contained a seventeenth-century passage in an unidentified cipher, titled Hermeticae Philosophiae medulla. With Sarah Lang and Megan Piorko, I identified the cipher, a Bellaso/Della Porta-style cipher whose 45-letter key itself forms part of the plaintext, and recovered the full text: 177 Latin words setting out a practical recipe for the Philosophers’ Stone, fitting the alchemical programme of the surrounding notebook pages.

Approach

The ciphertext and the cipher table in the manuscript both contain copying errors, which had to be corrected first. The key turned out to be a line of Latin verse from Giovanni Aurelio Augurello’s alchemical poem Chrysopoeia, which Arthur Dee had also written out on folio 12v of the notebook. The papers below give the transcription, the key and the full Latin text, and the C code used for the decipherment is on GitHub as ArthurDee.

Publications and media

Bean, R., Lang, S. and Piorko, M. (2022). Solving an Alchemical Cipher in a Shared Notebook of John and Arthur Dee. In Proceedings of HistoCrypt 2022.

Conference talk: HistoCrypt 2022 (R. Bean, presenter).

Invited talk with Sarah Lang and Megan Piorko: Decrypting the Secrets of Nature (slides), Ca’ Foscari University of Venice, 30 June 2026 (video).

Piorko, M., Lang, S. and Bean, R. (2023). Deciphering the Hermeticae Philosophiae Medulla: textual cultures of alchemical secrecy. Ambix 70(2):150–183. doi:10.1080/00026980.2023.2201744.

Bean, R., Piorko, M. and Lang, S. (2021). Deciphering the Philosophers’ Stone. The Conversation.

See also the full publications list and the presentations archive.