Blogger Sheryl Canter offers this Recipe for SeasoningCast Iron based on what looks like a very well-thought out scientific analysis. After researching the subject she concluded:

The seasoning on cast iron is formed by fat polymerization, fat polymerization is maximized with a drying oil, and flaxseed oil is the only drying oil that’s edible. From that I deduced that flaxseed oil would be the ideal oil for seasoning cast iron.

Here’s the short version of this post explaining the process:

  1. Clean the pan (read Sheryl’s advice on several options.)
  2. Heat the pan in a 200°F oven to be sure it’s bone dry.
  3. Pour a little flaxseed oil on a paper towel and thinly coat the pan.
  4. Rub the oil off with paper towels or a cotton cloth until it looks like there is nothing left on the surface. The pan should look dry.
  5. Put the oiled pan in a cold oven, set at 500°F . When it reaches temperature bake the pan for an hour.
  6. Turn off the oven let the pan cool inside the oven for two hours.
  7. Repeat the process several times.

Flaxseed oil is, apparently, pretty expensive and tends to go rancid quickly. Nature’s Way Flax Oil – 24 Ounce is reasonably priced ($0.25/oz) on Amazon and should be enough to season a lot of cast iron.