Iron. Oil. Heat.
These are the three foundational ingredients needed to season any cast iron pan.
If you have a cast iron pan, a bit of oil, and a heat source then you should be able to season that pan. And so the simple answer is, yes, if your heat source is a campfire or a gas grill this would count and you should, most definitely, be able to season cast iron outdoors on a grill or other open flame.
In fact, in my own experience, I’ve had some great luck seasoning cast iron both on the barbecue and over the fire while out camping. There are many practical benefits including dispersal of smoke, efficiency of the process, and the honest-to-goodness joy of sitting around a fire doing something as practical as seasoning your cookware.
I’ve also had a couple bad experiences. So, a caveat…
Cast Iron Guy Caveat: Fire and flame are less predictable than electric heat sources. And unpredictable heat can mean things might get a little too hot or too cool as you work to find the just right level of heat to achieve the best seasoning results.
Too low heat means that the chemical reactions to create seasoning won’t happen and the oil will likely just get gummy and sticky and fail to properly polymerize to become seasoning.
Too high heat means the oil and any established seasoning will likely burn and disintegrate leaving bare iron behind.
Check out my article on using a self-cleaning oven to strip seasoning for a refresher on how different levels of high heat affect the seasoning on a pan. I wrote about some of the chemical properties of seasoning and how the blast furnace temperatures of self-cleaning modes torch seasoning to ash.
Finding that just right heat in an oven somewhere in the middle of that too high and too low value is a matter of setting the knob to the just right number.
Finding that just right heat on a campfire or over a gas flame is a trickier prospect and requires attention and care above the heat source, and definitely not just throwing it into the flames or coals and hoping for the best!
While many things can go right, there is more wiggle room for things to go wrong: uneven seasoning, soot and ash contamination, over-heating and burning off the seasoning you’ve already created, increased difficulty to season handles or edges, or even in the extreme, possible cracking of your pan by moving it through too much temperature variation too quickly.
So, with a good steady-burning bed of coals or a medium flame on your grill, a rack or grate to rest your pan above the heat, the right tools, the right oil, and with work and care, yes, you can season cast iron on a campfire or outdoor grill… but maybe start with a practice pan to learn.