Cast iron cookware does not feature a synthetic coating. Instead, its nonstick surface consists of polymerized fats cross-linked directly to the porous surface of the iron. This protective seasoning patina forms through repeatedly heating unsaturated fatty acids past their smoke points until they transform into a tough, glass-like plastic layer.
When you scrub with coarse kosher salt, you deploy a mineral with a Mohs hardness of roughly 2.5. Polymerized linseed, canola, or grapeseed oils register a comparable surface resilience. As long as the scrub is performed without high-speed power tools, the salt crystals shatter and round off before gouging the seasoned iron beneath. Fine table salt fails here; its tiny grains dissolve too quickly and lack the structural facets required to lever stubborn crust off the cooking surface. Coarse salt crystals act as millions of tiny chisels, applying localized shear force straight against carbonized debris.
Because sodium chloride does not dissolve in lipid environments, pairing salt with neutral cooking oil creates an aggressive yet lubricated paste. The oil suspends loosened grit, reduces localized friction heat, and coats the raw metal exposed during heavy food release.
