Pharmaceutical Preparation Class Structure in the Voynich Manuscript Balneological Section (f75r–f84v): A Four-Zone Directional Gradient Consistent with Medieval Balneological Protocol

The balneological section of the Voynich Manuscript (f75r–f84v, 20 folios) has been variously interpreted as a bathing scene catalog, a gynecological illustration series, or an alchemical process diagram. We present a systematic class opener frequency analysis across all 20 folios that reveals a directional four-zone preparation class gradient incompatible with a purely decorative or random arrangement. Zone 1 (f75r–f76v) is dominated by syrupus-class vocabulary (oral pre-bath preparation); Zone 2 (f77r–f79v) by qualified compound vocabulary (constitution-specific compound baths, six consecutive folios); Zone 3 (f80r–f82v) by oil-class vocabulary (post-bath oil and powder treatments, six consecutive folios); Zone 4 (f83r–f84v) returns to syrupus at exceptional density (f83r: s=29, the highest single-class count in the entire section), consistent with a final oral consolidation protocol. The folio at the exact midpoint of the section (f79v, folio 10/20) contains exceptional figures absent from all other folios — a woman-fish figure (mermaid), a figure with a cross, and a figure with a ring — and has no substrate comparator match, consistent with its role as a structural boundary marker between Zones 2 and 3. The preparation class citation authority Pietro d'Abano (Conciliator differentiarum philosophorum et medicorum, 1303/1521) is present on all 20 balneological folios without exception, constituting the strongest bibliographic signal for iatromathematical medical context in the Voynich Manuscript HAIL-P-004, DOI 10.5281/zenodo.20392093; Paduan Medical Reference dataset, DOI 10.5281/zenodo.18687530, August 2025 — public-record priority anchor. A per-image figure typology audit of all 20 folios identifies two distinct illustration formats (COMMUNAL POOL and CASE ENTRY) and two explicit catalog row typological displays (f80r: 7–8 labeled figures; f82v: 5 labeled figures), consistent with a structured patient typology reference system. The four-zone structure is consistent with the claim that pool structures encode treatment routes by constitution class, and with the broader court physician workflow hypothesis HAIL-P-009, DOI 10.5281/zenodo.20391967. --- Substrate origination documented August 2025 (Paduan Medical Reference dataset; DOI 10.5281/zenodo.18687530, copyright origination 2025-08-27).