I'll preface this post by saying it's long and very detailed. If that type of post isn't what you like, then stop now and go read something else that isn't as technical as this post is. For those who like to learn about specifics in how their cookware is made and what level of quality it is, continue. You may learn a lot of information you didn't know.
I've seen a lot of posts about the types of metals and why some are better than others for cooking using various methods.
This link is to a PDF, (Portable Document Format), that shows the surface of many of the most popular types of cooking metals, under extreme magnification. I thought it might be helpful to those who attempt to explain why some types of metals are better than others when using them under specific circumstances.
First, I have to point out a few things about the subject. The best way to begin is to explain my credentials concerning the subject.
I worked for a major aircraft manufacturer as a process improvement specialist. Each area of manufacturing that fell within my sphere of knowledge, was assigned to me to examine in minute detail, and if possible, improve the processes and training for that area.
My specialty was metals. During a decade span, I re-worked the shot-peen, bead-blast areas that worked with steel and aluminum mostly. I also improved the heat-treating areas that worked with steel and aluminum. The electroplating areas were my last effort for the company before becoming bored with this line of work and switched to Database design and management for my last 10 years with the company. I worked as an Aircraft Electrician the first 5 years, trouble-shooting the wiring installation on new aircraft prior to test flights. After I learn a subject, I get bored with it easily and look for new challenges.
Ok, that said, I know metals. Steel and Aluminum especially. What I say on the subject isn't off the top of my head, but a result of learning many thousands of details about how these metals are made, formed, treated and used.
The grade of metal is determined by it's mixture of alloys and how they are formed into the final product. There are many types of mixes for each type of metal, but most consumer level metal products are made from just a few blends of alloys and treated using only a few methods.
This is what makes "Better Metal" that you've all heard of when buying cookware.
Some metals are made with higher levels of the less expensive alloys and treated using only brief, low quality standards. The resulting product can be an uneven mix of substances that again result in low quality end products. These are your $1.99 pots and pans made somewhere in Asia using who-knows-what manufacturing processes.
Pots and pans are made using many different methods of layering metals. This is mostly to improve the products life-span, heat dispersing and cooking surface properties.
Starting from the surface and working downward:
Very basically, the smoothness of the surface and its porosity are the factors that have the most influence on how food reacts when placed on the metal under varying circumstances.
Cast Iron is very porous. It's the nature of the process used to form it. You'll notice in the magnification photos that it's also very uneven. This surface, when used with oils, is able to retain a lot of oil in the pores of the metal, causing the food to literally "float" above the metal while cooking. If the cast iron is allowed to rust to more than normal, (all cast iron has rust on and in it), then that rust will interfere with the smoothness of the surface and cause roughness that will in turn cause foods to "stick" to it by becoming embedded in the pores after being gripped by the oxidized iron particles.
Try cooking on a rusty cast iron pan. The food will stick like glue.
Some cooks, (like me), never let their cast iron touch water. Not while cleaning or cooking. The pores of the iron are kept full of oil and not allowed to rust hardly at all. The pores remain pretty clear of rust.
When you wash a cast iron pan in water, the oils are removed from the pores and water allowed to penetrate into the pores. This will allow almost instantaneous oxidation, (rust), to develop down inside the pores of the metal. At that point, you can wipe, scrub, and scratch all you like, the rust is there to stay. The best you can do is oil the surface and hope that the expansion of the metal will work most of the rust out during cooking, and into your foods. Then, as long as you don't put water on it again, the rust will break up and move to the surface and out of the pores eventually. Better to use salt and oil to clean the pan and then to wipe it clean of salt as much as possible and put a continuous coating of oil covering the cooking surface. This will fill all the pores with oil, not rust.
There are different qualities of cast iron and different surface qualities to it as well. With cast iron cookware, you mostly get what you pay for unless you get lucky at a thrift shop or yard sale.
High porosity, low porosity, high finish, low finish, cast grade, alloy quality...they all have to do with the quality and performance of the end cookware product. Just because it's cast iron and *looks* the same, doesn't mean it *is* the same.
Well, I'll put that link here now and tell you that it covers many other types of cookware other than cast iron. I'll talk about them in future posts in this thread.
If you made it this far, congrats. Most people won't. With most, the desire to learn is compromised by the effort it takes to do so.
Here's the link to the magnification photos.
The photos themselves say a lot.