How cast iron tubs are made
HOW ARE CAST IRON TUBS MADE?
Cast iron tub production is a relatively inexact science and hasn't really changed that much over the past 150 years. While acrylic tubs will look almost uniform and perfectly formed, the very nature of molding and enameling cast iron tubs makes any real uniformity impossible.
First in the process of production is pouring molten iron into a mold. When finished and after cooling, the casting will be fairly rough and there is a lot of finishing required to remove sharp ragged edges.
After cleaning up and smoothing all the edges, the basic molded tub is again heated up to be red-hot at around 850 degrees Celsius. It is then quickly removed from the furnace and placed into an area where the enamel, in a powdered form, is sprinkled onto the inside of the tub mold. This process is normally repeated between three to five times to ensure a minimum thickness and relatively consistent layer of enamel deposit is in place.
This is the reason cast iron tubs have an uneven appearance on the enamel surface and sometimes undulations on the edges.
Due to their extreme heavy weight, most cast iron tubs do not need to be attached to the floor.