I'm a little late to this, but it's called seasoning (or reseasoning) and you can either try to take it down all the way to bare metal or just work on building

I'm a little late to this, but it's called seasoning (or reseasoning) and you can either try to take it down all the way to bare metal or just work on building up additional layers. Plenty of articles available for either, I'm sure I'm leaving things out. Don't get too distracted by fancy processes, remember this is something people have been doing for hundreds of years. If you want to go bare-metal and have an oven with a self-cleaning cycle, that's probably the simplest way to go - put the cast iron in there open-side down and run that cycle. I'm not sure just how much smoke this will release, but you might not want to do it on a day when you can't open windows. I've also seen notes that this can sometimes cause warping, so buyer beware. To build up the seasoning, it's basically going to be multiple repetitions of putting on a thin layer of a high-smoke-point food-safe oil, heating and repeating. Darker color generally just indicates more layers. In some ways it's almost like you're varnishing the cookware with an oil-based varnish, but without some of the other components of varnish. A lot of guides will recommend flaxseed oil for seasoning, it's also known as linseed oil and used to be pretty common in varnishes and wood finishes. For a contrary (and easier and cheaper) view, see https://www.reddit.com/r/castiron/comments/5owtnm/why_i_dont_recommend_flax_seed_oil/ https://www.reddit.com/r/castiron/comments/5owtnm/why_i_dont... (see also https://en.wikipedia.org/wiki/Drying_oil https://en.wikipedia.org/wiki/Drying_oil about oil-based varnishes)