Here in the western U.S., cast iron utensils, (skillets, dutch ovens, etc.) are a way of life.
We've found what appeared to be totally useless cast iron items at auction sales and have turned out practically new looking ones with this simple method.
If the piece has a lot of built up "gunk", it's best to use a wire brush to remove any loose cooked on grease and dirt (outside of course). Then, remove all the racks in an electric self-cleaning oven. Place aluminum (excuse me, aluminium) foil under the burner on the bottom (to catch any drippings). Then replace only one rack just above the burner coil and place the item(s) upside down on the rack. Turn it on to self-clean for a minimum of 2 1/2 hours... maybe even 3 1/2. It'll smell and maybe even smoke a little so it's nice if you have a ventilator fan in the kitchen.
When the oven goes off, let it cool until the safety lock on the oven door releases. Then, carefully with a hotpad, remove the pans and let them cool a little more. Then coat them inside and out with 2 or 3 coats of a solid cooking shortening such as Crisco, etc. After the 3rd coat, replace in the oven and turn it on to about 300 degrees (F) for maybe 30 minutes and then turn it off until the oven cools down... Voila! new cast iron skillet...