The majority of the fire pits and fire bowls are made from 3mm thick steel.
The bowls are not treated in any way as a coating of heat resistant paint would still burn off and deteriorate over a period of time. They have been rubbed over with oil and will eventually oxidize becoming a deep autumn color. However the steel is so thick this has no impact on the fire pits long term durability. The fire pits and bowls can be rubbed with a wire brush and then oiled over however it is fine to simply leave it outside and let it take its natural course.