White cast iron is characterized by the prevalence of carbides, impacting; high compressive strength, hardness and good resistance to wear.
Gray cast iron is characterized with graphite in the microstructure, giving; good machinability and good resistance to wear and galling.
Ductile cast iron is gray iron with small amounts of magnesium and cesium which nodulates the graphite, resulting in; high strength and high ductility. Very similar to malleable cast iron but pieces can be cast larger. Ductile cast iron is the newest form of cast iron and is also called nodular cast iron.
Malleable cast iron is white cast iron heat-treated to improve ductility. Malleable cast iron is more like mild steel but is limited in the size that things can be cast because it starts with white cast iron.
Not being an expert in metals or metallurgy I will now try to describe some of these terms.
Ductility is the irons ability to withstand bending or twisting pressure without fracture, while malleability being very similar to ductility is the irons ability to deform when compressed and not fracture. Galling is the irons ability to not form a lumpy surface e.g. when welding. Nodulates refers to the graphite in the iron forming round balls instead of flakes which helps to prevent cracks because of greater distance between balls as opposed to flakes.
What does all this mean? I don't know. But cast iron cookware is made from gray cast iron according to everything I've read and it is fairly easy to obtain this information online. There is no such thing as black iron. But my cookware is black you say. Yes it is, from the carbon formed from the grease or oil used to season it.
The only way to tell what kind of iron is used to make something is to break it. Once the iron item is broken then you look at the break to see what color it is. If the break is white you have white cast iron, if the break is gray you have gray cast iron. Another way I know that cast iron cookware is made of gray cast iron, I've received enough broken pieces to be able to look at enough cast iron cracks to tell you they really are gray.
Now all these so called experts who use the term black iron are just plain wrong. One of the experts who helped to form one of the largest cast iron collecting groups and has written the bible on cast iron collecting, references "Principles of Metal Casting" and "Casting and Forming Process in Manufacturing" in the bibliography of the bible, this guy calls it black iron within the bible. How can this be? I don't think he actually picked up either of the books he cited to make his work appear more impressive.
Another of these experts and co founder of the same large cast iron collectors group is supposedly an educated (he has a doctorate and works for a prestigious university) man, he calls it black iron. This guy even refers to himself as the Black Iron Dude. If he were a black man it might be O.K. to call yourself the Black Iron Dude, but he isn't a black man, he is referring again incorrectly to what cast iron cookware is made of.
Enough ranting on my part but I think you should at least try to get your terminology correct. Get the terminology correct especially if you are a noted national voice or so called expert in the field. If you are out there educating others you should be giving them the correct information.
