This name is applied to sheet iron of very highly polished or glazed surface also known as planished iron.

It is used for protecting the lagging of engines and boilers and for other uses where a non-corroding black iron of finished surface is desired.

These sheets are made by piling together about fifty pickled sheets of soft steel with powdered charcoal sprinkled between adjacent sheets. The pile is wrapped in old sheets, wired and heated in a furnace to a cherry-red heat for about 6 hours. Upon cooling, each sheet is swept free of loose charcoal and is then sprayed with steam to form a thin oxide. Again the sheets are piled together, heated and then placed on the hammer table, several in a bundle, and pounded with a steam hammer. This brings about a grinding action which grinds the carbon and oxide on the surface down to a highly polished coating.