Natural Finish: The piece is taken hot from the forge and left to cool. This leaves a scale which will protect the piece somewhat. If used for an indoor application it would be fine.
Shine Finish: The piece is taken hot from the forge and shined with a wire wheel to remove most of the scale to give the piece a shine. But, the piece no longer has any protective coating and must be clear coated to protect from rust.
Rust Finish: The above process is repeated, but instead of clear coating a series of chemicals is applied to rust the piece and to stop the rusting process. It is then clear coated.
Hot oil and wax: The piece is removed hot from the forge and wire wheeled to remove scale. It is then dipped in a hot mixture of linseed oil and beeswax, which is absorbed into the steel. The piece is then treated with a wax for additional protection.
Easy Black: The piece is removed from the forge hot and wire wheeled to remove scale. A chemical is applied turning it black and the same wax is applied. I don't suggest this finish for exterior use, as the wax is the only protectant and must be reapplied regularly.