If cast iron is left in the sink to soak, put in the dishwasher, or allowed to air dry, it will rust. It can also happen when you store your cookware in moisture-prone environments, such as a cabinet near a dishwasher, an open cabinet in a humid location, or stored outside.
Cast iron famously seasons itself with cooking because the oils bake onto the pan. But over-enthusiastic scrubbing, acidic foods, or excessive heat can break down that seasoning. It's a good idea to reseason your skillet a couple of times a year or any time you notice the surface of your pan drying up or rusting.
Keep It Seasoned
Seasoning cast iron is an easy process which makes it different from other pans. You season it once and it's good for decades.
Black Residue
There can be residue from the seasoning that may come off your seasoned cookware. The residue is not harmful in any way and will decrease as the cookware is used over time.
Eggs fall into the category of sticky foods that are not ideal for cast iron skillets that haven't built up their seasoning yet. While cast iron can become non-stick with sufficient use over time, a newer skillet will almost certainly cause your eggs to stick to its porous surface.
Cast Iron: 1204°C (2200°F)
Since olive oil is such a pantry staple, many people naturally wonder if they can use olive oil to season cast iron. You can use olive oil to season cast iron, but you need to choose a high quality extra virgin olive oil, which should have a smoke point close to 400 degrees Fahrenheit.
Cast iron is in a crystalline metal state, where cracks can very easily grow on crystal boundaries. This makes the iron 'hard' but very brittle, and highly likely to crack and break if dropped or thermally shocked.
The seasoning will only burn off at about 800°F, so don't worry that you will damage your pan by cooking with high heat. Cast iron can, however, easily get too hot for the dish that you're trying to cook.
A cast iron skillet can almost always be brought back to life and its age is often seen as pro rather than a con. That's why thrift stores and estate sales are great places to find cast iron skillets inexpensively.
Two words: heat & oil.
The most common reason food sticks to cast iron is because the pan is simply too hot. Because cast iron retains heat much better than other types of cookware, you generally don't need to use as high of a heat setting as you normally would with stainless steel or aluminum cookware.
Cast iron shines when it comes to high-heat cooking, like searing steaks or charring vegetables, but it goes beyond that—you can use cast iron to sauté, bake bread, or even or make a table-worthy dessert.
Caring for Cast Iron
With soap if it needs it. Scrubbing with the rougher side of a sponge if it needs that to remove food particles. Don't use steel wool, and do dry it completely. Then, put another tiny bit of oil in and rub it all over, wipe it away, and put it over a burner for a few minutes.
The vinegar solution will dissolve the rust, but once that's gone, it can penetrate further and start eating away at the original cast surface of the pan, the ultimate death sentence for your skillet. If that happens, retire it to a piece of farmhouse-chic kitchen decor.
Common cooking oils like olive oil will gradually produce seasoning, but won't be as effective as grapeseed oil. Canola, other vegetable oils, and shortening are a little better.
Over-cleaning your cast iron pan is unnecessary and will only stand to damage your seasoning.