Using a set of commercially prepared sodium ferrocyanide absorbers enriched to 91.2% Fe57the Lamb‐Mo¨ssbauer factor was measured to be 0.28±0.03. The thickness of Fe57for these absorbers was measured using x‐ray absorption techniques and was found to be considerably smaller than that advertised by the manufacturer even after correcting for the size of the ferrocyanide particles in the absorbers.