Clean the pan. Use a steel wool scrub brush to getting all of the residue out of the pan. This takes some elbow grease. In some cases, you may get down to the bare, cast metal, and that's OK. Note that exposed metal will "flash rust" quickly...no worries that superficial rust comes off when the next step is applied.
Wipe the pan with a liquid oil, like Canola or vegetable oil. I use flax oil because it has a lower smoke temp, and it plasticizes well. Use a papercloth to apply the oil in a very thin layer. Then use a second, dry, paper towel to wipe the surface again. Do this on all surfaces: exterior, interior, handle. The surface should be shiny, but barely wet to the touch. There should be no pooling of oil.
Put the skillet in the oven, upside down, for one hour at 500 degrees. A drip tray underneath the skillet is optional. Note that this step can be a little stinky. Make sure that the kitchen is adequately ventilated.
Let cool for 1+ hours in the oven. Take the pan out of the oven and let it cool to room temperature. Repeat the process of applying oil and heating 4-6 times.
