See-through leaf: front/back alignment of the Voynich herbal leaves (88 pairs) and a preregistered blind test of the "root traced through the parchment" hypothesis - with results

Registered-report style deposit. (1) Data and code of the page voynich.site/see-through-leaf (published 7 October 2026): the mirrored back of each regular leaf of the Voynich manuscript (Beinecke MS 408) aligned to its front by the parchment edges on the Yale scans - an alignment table for 88 leaf pairs and its generator. (2) An observation made with the tool - the roots of the plants on the two sides of a leaf fall at the same height - and the hypothesis that the root was traced through the parchment from the other side (the leaf lit from below), which would explain the "confused roots" of the herbal. An exploratory check with crude ink masks (included, with its null result) is followed by a preregistered blind test: the coder marks one root box and one neck point per page in shuffled order, blind to the pairing; measures (box IoU, neck distance, neck height), a permutation null over pairs, power and composition controls and the decision rule are fixed here before any answer. The scoring script and the coding form are included; the order key is withheld until coding is complete and committed by MD5. v2.0 (8 October 2026) adds the results: all 124 cards coded (118 pages + 6 duplicates, duplicate IoU 0.53-0.96), the order key (MD5 matches v1), the raw answers and the scoring report. Box IoU of front and mirrored back 0.302 against a permutation null 0.273 (p 0.0115), neck distance p 0.54, neck height p 0.0075 - none passes the preregistered per-measure threshold 0.0033, while a synthetic tracing is detected in 100 % of repetitions. Verdict: the hypothesis that roots were traced through the parchment is NOT supported; the similar root heights on the two sides reflect page layout. Nothing in this deposit reads the text of the manuscript or identifies any plant. Scans: Beinecke Library, Yale (public domain), via archive.org. Licence CC BY 4.0 (code also MIT). Project site https://voynich.site.