REFINISHING CAST-IRON COOKWARE:
Photos from a recent restoration project are shown at the end of this article
1. Remove all traces of rust on your antique pan. You can use a wire brush, coarse steel wool, or wire bonnet that you attach to a power drill. A final wipedown with CLR cleaner will remove residual deposits.
Depending on the amount of rust this may be a small amount of work or a full day job. DO NOT USE MACHINE OIL OR ANY OTHER harsh cleaner as this will taint the metal.
2. Rinse pan with very hot water. DO NOT USE SOAP.
Dry immediately with paper towel and inspect all areas for rust. This includes tight corners around handle and the hanger eyelet.
If there are still traces of rust, repeat step 1.
3. Remove carbon build-up. If you have large areas with carbon build-up you can remove this by throwing the pan in your fireplace over a lit mound of newspaper or dry leaves. Fire for 1/2 hour.
Old-timers used to clean their pans every few years by putting them on a dry leaf pile and burning it until the metal was shiny. This method doesn’t produce intense heat, which will risk warping or cracking your pan.
Another method that produces great results: Your oven set to the auto-clean cycle. Leave the pan in until it completely cools and make sure your oven vents to the outside of the house. This puts off a LOT of smoke. When done, simply wipe down with clean hot water and a sponge. Re-season as instructed.
You can also use a portable propane torch – provided you take care not to get the metal too hot, risking warping or cracking the pan.
My dad told me stories of my grandfather who used beach sand to strip any built-up gunk or rust from his pans.
Regardless of the method for removing rust or buildup – properly taken care of pans should never rust again.
4. Cleaning and seasoning. Once you have ensured that all traces of rust are removed from the surface, it is time to clean, season and seal the surface of the cast iron. Scrub all remaining residue off the iron with a scrub brush and a little dish soap. Ensure that it is rinsed clean in very hot water. IMMEDIATELY make sure the pan is completely dry and free of rust, uneven buildup or other residue (rust will set in again on bare metal within 5 minutes.) Use wads of paper towel to remove any residue until they wipe clean. Heat your oven to 375 degrees. Place pan in preheated oven for 15 minutes.
Remove and evenly coat surface (USE CAUTION, IT’S HOT!) with plain vegetable oil or rendered bacon fat. Less is more with this process. Wipe away any excess, ensure that all exposed surfaces are evenly coated and place back in the oven for no less than one hour. TURN ON YOUR EXHAUST FAN and open your windows. The pan will smoke slightly. This is normal.
Turn off the heat and leave the pan in the oven until cool. If you see a vegetable oil buildup, you used too much. Heat pan again as shown above and wipe excess off with paper towel.
5. Care and use. Congratulations! Your pan is now seasoned. The first few times of use, avoid cooking overly-acidic foods like tomatoes or vinegar-based products. Also avoid boiling water until the surface cures. If you should smell rust when inspecting the pan or taste a metallic residue, repeat the above steps to ensure it is properly seasoned.
NEVER clean a hot pan with cold water. Never quickly immerse a hot pan in dishwater. Allow the pan to cool slightly to avoid thermal shock which will warp or crack the iron. When allowed to cool slightly, run hot tap water or boiling kettle water in the pan and scour with a bamboo or plastic bristle brush.
Pans that exhibit thermal shock may be warped to the point of not sitting level on a flat glass stove top. Once warped, there is no way to fix the issue. Take care and ensure that your pans become treasured heirlooms. They, in turn, will give you a lifetime of memories.

A badly-neglected Wagner skillet with extreme corrosion and carbon buildup. Amazingly enough, even this clunker can be restored to a usable piece of cookware.

Scouring out rust and carbon buildup using 220-grit sandpaper. Move on to 600-grit to smooth out the scratches. Then finish off with steel wool.

Corroded Wagner stamp on a cast-iron skillet. Take care not to sand out the maker mark when restoring a finish. (This pan was manufactured in the Depression era so there's a fair amount of history!) Use a Dremel and a fine wire wheel brush with a light touch for detail work like this.

Scouring a cast-iron pan with steel wool and CLR cleaner. Rinse well with very hot water after all traces of rust are removed. Then dry and heat immediately.

A properly-scoured cast-iron pan. All pitting, scratches, corrosion and carbon buildup should be removed.

Using a propane torch to remove built-up carbon. Carefully heat until the carbon turns white-hot and converts to ash. Keep the torch moving! Don't heat up one spot too much or it will warp. When cool, wire brush off the gunk or scrape with a utility razor.

Preheat your newly-scoured cast-iron pan in the oven at 375° for 15 minutes. Then wipe down with vegetable oil and bake for 1 hour. Let cool before removing.

New vegetable oil finish on a cast-iron pan. It will take months of regular use to blacken and cure rock hard. Avoid cooking overly-acidic foods or boiling water the first few times of use. After that, they're pretty much low maintenance when cleaned properly.

A newly-finished antique cast-iron dutch oven pot cover. A dremel and wire wheel brush worked well for removing the carbon buildup around the stamping. The speckled caramel color is normal and will darken over time. The dark spots are residual carbon that protect the iron. Note the consistent, even application. Eventually, it will all turn jet black.