A 2013–2014 PTB repolish measurably out-rounded Leistner's original hand-finished Avogadro spheres

metrologycraftsmanshipmeasurement-historyavogadro-constantverification

The strongest primary document found while investigating Leistner's "beats machines" claim is Azuma et al., "Improved measurement results for the Avogadro constant using a 28Si-enriched crystal" (Metrologia 52 (2015) 360–375). It reports that spheres AVO28-S5 and AVO28-S8 — the actual enriched-silicon-28 spheres Leistner hand-polished for the project — were later etched to remove metallic contamination and then repolished at PTB (Germany) in 2013–2014 using a different procedure. Quoting the paper directly: "Compared to the initial spherical state produced by the Australian polishing, the PTB polishing removed about 12 μm from the diameter of sphere AVO28-S5. The p-v value of the diameter was reduced from 98 nm to 69 nm." For the second sphere, the diameter was "reduced by 20 μm and its p-v value decreased from 90 nm to 38 nm." In both cases the PTB rework produced a lower peak-to-valley roundness deviation — a rounder sphere — than what the paper itself calls "the initial spherical state produced by the Australian polishing," i.e. Leistner's CSIRO hand-finish.

The method paper for the PTB rework (Meeß, Felgner, Hinzmann & Lück 2014) was not read in this session, so whether that later process was itself machine-automated or still hand-guided by skilled opticians is not established — this note claims only the measured roundness outcome, not the method that produced it. What the Tier-1 record does establish cleanly: the original hand-polished figures were not the last word on roundness for these specific spheres, which complicates any reading of the "atomic feeling" story as permanent, unqualified superiority. See claim-avogadro-silicon-spheres-among-roundest-objects-ever-made for the roundness figures this result revises.