Step 2: Cleaning Cast Iron
All pieces of cast iron must be cleaned before using them in the kitchen. New pieces of cast iron (bare or "pre-seasoned") usually have a thin coating of wax on them to keep them from rusting on the store shelf. Pieces from yard sales or flea markets are most likely very dirty also.
For the first cleaning of a piece of cast iron, it is OK to be a little rough, but remember - never use soap or detergent on cast iron. Also, never put cast iron in a dishwasher. They must be cleaned by hand. The more often cast iron is used, the faster it will build up its own natural non-stick surface (called the "seasoning") and the easier cleaning will become. However, it should be scrubbed well on the first cleaning. The reason for not using soap is simple - on a microscopic level, cast iron is very rough with many crevices for soap to get into. It will stay in there and make food taste like soap. Instead, it is necessary to let it naturally build up the seasoning that will bond to and fill the crevices.
Cleaning is simple - use hot water. The hotter, the better. A sponge with a smooth side and a scouring side works well for this. For the first cleaning, scour it well to remove any wax, stale oil and other bits of built-up grime. Small spots of rust can be scoured until the rust washes away. Problem spots of rust can be rubbed off with a small piece of sandpaper or some type of rotary tool. But remember - bare spots of metal will be very likely to develop rust rapidly, so use care.
After the first cleaning, all other cleanings should be more gentle, with a soft cloth or sponge. Stuck-on bits of food can be left to soak for a few moments in a sink of plain water or scoured off, but remember - you will be scouring away the seasoning that you are trying to build up.
In this photo, I am cleaning a new bare cornbread sheet, a new pre-seasoned bean pot and an old, used pan.