Fortuna is made entirely from black bright boards OL37 with a thickness of 1 / 2 / 3 / 4 / 5 mm and is has fire-clay lining. It is varnished in two layers.
Hercules firebox is made from casting FC200 and black bright boards OL37 with a thickness of 1.5 / 2 / 3 mm and firebox fire clay lining.