Historical evidence for the use of the skullcap in the 13th century can be found in pictorial sources such as the Maciejowski Bible manuscript, as well as in archaeological finds, which show that it was frequently worn under the great helm or over a chainmail coif. To protect the non-stainless steel from corrosion, the helmet should be wiped dry after each use and regularly rubbed with a thin film of gun oil or acid-free machine oil. Dry storage and the occasional removal of surface rust with fine steel wool or a polishing paste are also recommended.