How to Season a Carbon Steel Pan
Unless it comes preseasoned, a carbon steel pan requires seasoning just as a cast-iron pan does. This process bonds oil to the surface, providing protection against rust and making the pan nonstick. (Flaxseed or sunflower oil is best, but any vegetable oil will do.) The instructions that come with our winning pan suggest an unusual method, but we found that it really works.
Initial Seasoning
First you’ll need to remove the new pan’s wax or grease coating (used to protect the metal from rusting in transit). Use very hot water, dish soap, and vigorous scrubbing with a bristle brush. Dry the pan and then put it on low heat to finish drying. Add 1/3 cup oil, 2/3 cup salt, and peels from two potatoes (these help to pull any remaining wax or grease from the pan surface). Cook over medium heat, occasionally moving the peels around the pan and up the sides to the rim, for 8 to 10 minutes. (The pan will turn brown.) Discard the contents, allow the pan to cool, and wipe with paper towels. You are ready to cook. (If you experience sticking, repeat once.) This method will work on any carbon steel skillet.
Routine Maintenance
Rinse with water, scrubbing gently with soft-bristled brush or sponge if necessary; avoid soap or abrasive scrubbers. Dry skillet thoroughly over warm burner. If kitchen is humid or you don’t use skillet often, apply very thin coating of oil to surface to prevent rusting.
Reseasoning
If cooking surface feels bumpy or has tacky residue (caused by partially polymerized oil) or patina is chipped, scrub with moderately abrasive sponge (also use a little soap if skillet is tacky) until patina feels even to touch (color does not need to be even).
Next, apply 1 to 2 teaspoons oil (depending on skillet size) over surface of clean skillet. Wipe away as much oil as possible with paper towel (excess oil will lead to tackiness); reserve paper towel. Heat skillet over medium heat, watching for oil to bead. Using tongs, wipe away beaded oil with reserved paper towel. Continue to heat, wiping away beaded oil, if any, as necessary, until skillet smokes (indicating oil breakdown). Let skillet smoke for 2 minutes. Turn off heat and let skillet cool.
Source:
https://www.cooksillustrated.com/how_tos/9588-how-to-season-a-carbon-steel-pan