I wrote about my struggles with this previously, and while my conclusions in that last blog post aren't all wrong, they're not all right, either.
But hey, instead of me taking the time to write out my experience in my words, how about I just refer you to this guide from Kenji Lopez-Alt, which will tell you all you need to know--and be correct, too: http://www.seriouseats.com/2010/06/how-to-buy-season-clean-maintain-cast-iron-pans.html
With regard to the mysterious flaking (or scaling, as Kenji calls it) that bedeviled my earlier efforts, here's the key, buried at the bottom of Kenji's post:
This happens when you heat the pan too often without adding extra oil to it. Rather than coming off in microscopic bits like normal seasoning will, the layer of polymers sloughs off in large flakes. To reach this state, I stored my pan in the oven for a month's worth of heating cycles without reoiling the surface in between heating. It's easy to avoid this problem by regularly oiling the pan after each use and not overheating it (don't leave it in the oven during the cleaning cycle, for instance), but once it happens, there's no turning back—you'll have to reseason it from the start. [My emphasis added.]That's it: Don't heat your seasoned wok or pan to smoking without adding oil or fat to it!
Also, when you heat up your pan/wok, swabbed with a very thin layer of oil, turn off the heat as soon as it starts smoking.
Other things about my previous post I'd amend:
- The stovetop method of seasoning your cookware definitely works just fine. Just don't heat your pan/wok without oil.
- Canola oil is actually a good oil for seasoning your cookware. It turns out the gunkiness that I (and others I've seen posting on the web) experienced with canola oil was due to not heating it to its smoke point when seasoning.
For more on the chemistry behind seasoning, and which oil is best, check out this blog post. She actually recommends food grade flaxseed oil, but it's expensive. But buried in her post is an allusion to how canola oil is decent since it's got some extent of the properties you want in the oil used for seasoning a pan.