Jeff Clark is 100% on the money. Mineral spirits, like all aliphatic solvents, leaves an oil coating. Use an aromatic solvent, such a xylol to clean the steel.( I would avoid the MEK, nasty stuff) ASTM tests call for a scribe line to be drawn in the surface to break any coating left by treatment or preperation. Next time clean and prep the surface, use an aromatic solvent to remove any trace of oils, apply each treatment, then score a line across the center of each sample. Rust should be measured along the edge of the score. Interesting test. Thanks for going the trouble.
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