White spots? Hard water. Gray spots? Bare iron.

White spots on cast iron are usually hard water stains; gray spots are bare iron where the seasoning has come off.

Hard water leaves calcium deposits when the pan dries. If you see white residue after washing, that’s it. Scrub with coarse salt or a chainmail scrubber, rinse, and heat the pan bone dry on the stove.

Gray spots mean your seasoning has flaked or worn away—common from cooking acidic foods like tomatoes, using high heat, or scraping with metal utensils. It’s not dangerous, just ugly. Scrub any rust off (baking soda and water paste works), then apply a super thin coat of oil and bake