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.
Famously durable, these pans are often passed down through generations. With proper reseasoning care, years of frequent use can actually improve the pan's “seasoning”—its natural nonstick coating. But sadly, cast iron skillets can indeed break.
Don't let it soak in the sink.
Cast iron is porous, meaning that long exposure to water can cause it to soak up the moisture and eventually rust. While a short soak won't do much harm, I avoid soaking the thing for fear of forgetting it and ruining the cure I've worked so hard develop.
Why can't you boil water in cast iron? When you have water at a constant boil in seasoned cast iron, the boiling causes the seasoning to release. This can leave patchy seasoning or an uneven layer of seasoning left on your cast iron.
If you accidentally leave your cast iron cookware on any heat source for too long, food, marinades, and sauces can burn and get stuck to the surface. The Fix: Use a pan scraper to remove stuck-on food. If the problem persists, simmer a little water in the pan for 3-5 minutes, then use the scraper.
Cast iron pans can leach a sizeable amount of iron into your food, exceeding dietary intake in some cases. Acidic foods will contribute to much more leaching while an old, heavily-seasoned pan will leach much less iron than a newer one.
Don't put cast iron in the dishwasher. Ever. The combination of harsh detergents, heat, and long stretches in the damp environment can destory years' worth of seasoning in minutes.
With proper care cast iron cookware can withstand a lifetime of use.
The black residue on a cast iron skillet isn't harmful; it's just a part of cooking with a cast iron pan. A black seasoned coating shouldn't rub off easily or affect the food, as it should form a useful non-stick surface for cooking. If residue starts to build up, however, this can affect your cooking.
Cast-iron cookware is porous, and the oil works to fill those pores and create a smooth, nonstick surface. Enough oil soaks into those pores during the initial coating, so you can go ahead and wipe off as much as you can. Leaving too much oil on is a common mistake that will leave your skillet sticky.
Don't ever store food in a cast-iron skillet
Additionally, although the idea of getting iron toxicity overload from cooking in cast iron pans has been mostly debunked, (via Livestrong) any food sitting in the pan for a prolonged period of time can develop an off, metallic flavor.
The acidity of tomatoes makes them challenging to cook in cast iron. Anyone who's ever eaten a tomato or cooked with tomatoes can verify that this fruit is quite acidic. As it happens, the tomato's acidity is precisely why doesn't work well with cast-iron cookware, especially for long cooking stretches.
Soap doesn't remove seasoning, but it can remove some oil.
Cast iron is beloved for its natural non-stick quality. This is built up over months and years of use, as a layer of seasoning develops on the pan's surface.
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.
Most often you can clean a cast-iron pan by simply wiping it down with a dry paper towel or cotton dishcloth. If the pan is well seasoned, bits of burnt, stuck-on food will come right off. If any stubborn bits remain, scrape them off with a plastic spatula.
Your cast iron can withstand heat - a lot of heat. A cast-iron skillet can withstand heats of up to 1500°F, which is much hotter than your oven could ever be. 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.
Enameled cast iron pots can sometimes develop white spots, which are often caused by cooking with starchy ingredients, like beans, or mineral deposits from water.
Cast iron seasoning is a layer of carbonized oil.
It may take a little extra care, but a well-seasoned cast iron pan will last for generations.
Heat to Alter Metal
Brass, steel, iron copper and silver can all be made weaker by heating the metal to a set temperature and cooling it slowly. It's not only used to create softer metal products but also more electrically conductive ones. However, it would be incorrect to state that heat always makes metal weaker.