Johann Gerlach, Occulta scripta chymica (Wellcome Collection MS.309): working transcription and decipherment, version 1

Working transcription and decipherment of Johann Gerlach, Occulta scripta chymica (Wellcome Collection MS.309, b19695561), an alchemical manuscript of 1572–1576 written largely in a simple substitution cipher, with plain-script parts in German and Latin. Status (November 2026). This is a working transcription, made with the help of an AI model (Claude, Anthropic), with doubtful sign and letter shapes checked on the images by G. Maranda. The cipher text (MS 7–207) agrees sign by sign with George Lasry's independent decryption of MS 7–10 and 13–30 at 99.64%, and a random sample of 30 lines checked by hand showed no errors. The plain-script parts were checked by independent AI readings and by a partial sample check by Dr Sarah A. Lang, but have not been checked by a palaeographer. Spelling conventions in the plain-script parts are not yet uniform. Every correction is listed under its page with its basis; decisions made by the AI on the image, not by a blind check, are marked as such. Corrections and comments are welcome and will be credited in later versions. Files: the deposit is split into five zip parts. Unzip all five into the same folder to obtain the complete folder Gerlach_MS309_deposit_v1; its MD5SUMS.txt lists a checksum for every file. Part 1 (core) holds the README, the transcription (TRANSCRIPTION_v13.md), the reading text (Gerlach_reading_text_v9.md), the cipher key and the scribe's alphabets, and the verification files, including checks that failed. Part 2 holds the code and trained sign-reader models. Parts 3a–3c hold George Lasry's CTTS files and decryption (unpublished working files, included with his permission) and the literature check. The main files are also provided unzipped for convenience. Prior work: the manuscript is listed in S. Lang, S. Zotov and M. Piorko, Sources of Alchemical Cryptography (HistoCrypt 2024), and in Adam McLean's database of alchemical manuscripts; neither reports a decipherment. Parts of the cipher text have printed parallels (B. Figulus, Thesaurinella Olympica aurea tripartita, 1608; J. Tancke, Promptuarium Alchemiae, 1614; and later prints), detailed in the transcription. Credits: George Lasry (independent decryption and symbol positions for MS 7–10 and 13–30, made with his CTTS tool, used with permission); Dr Sarah A. Lang (passed on Lasry's files and a student transcription, and made a sample check of the plain-script transcription); Svenja Wüstermann (2026, student transcription of MS 7, cited); Julius Kohn (1889, key written into the manuscript). Source images: Wellcome Collection, MS.309 (https://wellcomecollection.org/works/vq9e75rz), Public Domain Mark; not included. Image credit: "Johann Gerlach. Public Domain Mark. Source: Wellcome Collection."